Fictional technology is proposed or described in many different contexts for many different reasons:

• Exploratory engineering
  Exploratory engineering
  Exploratory engineering is a term coined by K. Eric Drexler to describe the process of designing and analyzing detailed hypothetical models of systems that are not feasible with current technologies or methods, but do seem to be clearly within the bounds of what science considers to be possible...
  
   seeks to identify if a prospective technology
  Technology
  Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...
  
   can be designed in detail, and simulated, even if it cannot be built yet - this is often a prerequisite to venture capital
  Venture capital
  Venture capital is financial capital provided to early-stage, high-potential, high risk, growth startup companies. The venture capital fund makes money by owning equity in the companies it invests in, which usually have a novel technology or business model in high technology industries, such as...
  
   funding, or investigation in weapons research.
• Propaganda
  Propaganda
  Propaganda is a form of communication that is aimed at influencing the attitude of a community toward some cause or position so as to benefit oneself or one's group....
  
   often emphasizes a speculative potential of a specific technology in order to stimulate investment in it, or a counter-technology. This is a common motivation in any society
  Society
  A society, or a human society, is a group of people related to each other through persistent relations, or a large social grouping sharing the same geographical or virtual territory, subject to the same political authority and dominant cultural expectations...
  
   dominated by a military-industrial complex
  Military-industrial complex
  Military–industrial complex , or Military–industrial-congressional complex is a concept commonly used to refer to policy and monetary relationships between legislators, national armed forces, and the industrial sector that supports them...
  
  . See also militarism
  Militarism
  Militarism is defined as: the belief or desire of a government or people that a country should maintain a strong military capability and be prepared to use it aggressively to defend or promote national interests....
  
  , technological escalation
  Technological escalation
  Technological escalation describes the situation where two parties in competition tend to employ continual technological improvements in their attempt to defeat each other. Technology is defined here as a creative invention, either in the form of an object or a methodology...
  
  , arms race
  Arms race
  The term arms race, in its original usage, describes a competition between two or more parties for the best armed forces. Each party competes to produce larger numbers of weapons, greater armies, or superior military technology in a technological escalation...
  
  .
• Advertising
  Advertising
  Advertising is a form of communication used to persuade an audience to take some action with respect to products, ideas, or services. Most commonly, the desired result is to drive consumer behavior with respect to a commercial offering, although political and ideological advertising is also common...
  
   which emphasizes some amazing potential of some technology that is "under development" (usually without any specific timelines) by a company that is seeking simply to present itself as being competent with technology. See also vaporware
  Vaporware
  Vaporware is a term in the computer industry that describes a product, typically computer hardware or software, that is announced to the general public but is never actually released nor officially canceled. Vaporware is also a term sometimes used to describe events that are announced or predicted,...
  
  , persuasion technology
  Persuasion technology
  Persuasive technology is broadly defined as technology that is designed to change attitudes or behaviors of the users through persuasion and social influence, but not through coercion...
  
  .
• Science fiction
  Science fiction
  Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...
  
   which explores the social or political or personal impact of some technology through storytelling
  Storytelling
  Storytelling is the conveying of events in words, images and sounds, often by improvisation or embellishment. Stories or narratives have been shared in every culture as a means of entertainment, education, cultural preservation and in order to instill moral values...
  
  .

• List of emerging technologies a more serious field.

Examples of such fictional technologies are:

• Reversible cryonics
  Cryonics
  Cryonics is the low-temperature preservation of humans and animals who can no longer be sustained by contemporary medicine, with the hope that healing and resuscitation may be possible in the future. Cryopreservation of people or large animals is not reversible with current technology...
  
  
• Simulated reality
  Simulated reality
  Simulated reality is the proposition that reality could be simulated—perhaps by computer simulation—to a degree indistinguishable from "true" reality. It could contain conscious minds which may or may not be fully aware that they are living inside a simulation....
  
  
• Mind uploading
• Molecular assembler
  Molecular assembler
  A molecular assembler, as defined by K. Eric Drexler, is a "proposed device able to guide chemical reactions by positioning reactive molecules with atomic precision". Some biological molecules such as ribosomes fit this definition. This is because they receive instructions from messenger RNA and...
  
  , Universal constructor
  Universal constructor
  A universal constructor may refer to*Universal assembler, a hypothesized nanotechnology device for building a large class of nanomachines including itself, or...
  
  
• Faster-than-light
  Faster-than-light
  Faster-than-light communications and travel refer to the propagation of information or matter faster than the speed of light....
  
   Travel, Warp drive
• Tachyonic antitelephone
  Tachyonic antitelephone
  A tachyonic antitelephone is a hypothetical device in theoretical physics that could be used to send signals into one's own past. Albert Einstein in 1907...
  
  
• Time travel
  Time travel
  Time travel is the concept of moving between different points in time in a manner analogous to moving between different points in space. Time travel could hypothetically involve moving backward in time to a moment earlier than the starting point, or forward to the future of that point without the...
  
  
• Space elevator
  Space elevator
  A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
  
  , Skyhook
• Transporter
  Transporter (Star Trek)
  A transporter is a fictional teleportation machine used in the Star Trek universe. Transporters convert a person or object into an energy pattern , then "beam" it to a target, where it is reconverted into matter...
  
  
• Terraforming
  Terraforming
  Terraforming of a planet, moon, or other body is the hypothetical process of deliberately modifying its atmosphere, temperature, surface topography or ecology to be similar to those of Earth, in order to make it habitable by terrestrial organisms.The term is sometimes used more generally as a...
  
  
• Dyson Sphere
  Dyson sphere
  A Dyson sphere is a hypothetical megastructure originally described by Freeman Dyson. Such a "sphere" would be a system of orbiting solar power satellites meant to completely encompass a star and capture most or all of its energy output...
  
  , Matrioshka brain
  Matrioshka brain
  A matrioshka brain is a hypothetical megastructure proposed by Robert Bradbury, based on the Dyson sphere, of immense computational capacity. It is an example of a Class B stellar engine, employing the entire energy output of a star to drive computer systems...
  
  
• Star lifting
  Star lifting
  Star lifting is any of several hypothetical processes by which a highly advanced civilization could remove a substantial portion of a star's matter in a controlled manner for other uses. The term appears to have been coined by David Criswell.Stars already lose a small flow of mass via solar wind,...
  
  

Many technologies were fictional for a long time before they became real, such as:

• hypertext
  Hypertext
  Hypertext is text displayed on a computer or other electronic device with references to other text that the reader can immediately access, usually by a mouse click or keypress sequence. Apart from running text, hypertext may contain tables, images and other presentational devices. Hypertext is the...
  
  , e.g. the World Wide Web
  World Wide Web
  The World Wide Web is a system of interlinked hypertext documents accessed via the Internet...
  
  
• rocket pack
• atomic bomb
• expert system
  Expert system
  In artificial intelligence, an expert system is a computer system that emulates the decision-making ability of a human expert. Expert systems are designed to solve complex problems by reasoning about knowledge, like an expert, and not by following the procedure of a developer as is the case in...
  
  
• genetic engineering
  Genetic engineering
  Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...
  
  
• radiological weapon
  Radiological weapon
  A radiological weapon or radiological dispersion device is any weapon that is designed to spread radioactive material with the intent to kill, and cause disruption upon a city or nation....
  
  
• mobile phones
• Quantum computer
  Quantum computer
  A quantum computer is a device for computation that makes direct use of quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. Quantum computers are different from traditional computers based on transistors...
  
  
• Artificial intelligence
  Artificial intelligence
  Artificial intelligence is the intelligence of machines and the branch of computer science that aims to create it. AI textbooks define the field as "the study and design of intelligent agents" where an intelligent agent is a system that perceives its environment and takes actions that maximize its...
  
  

There are also technologies that have been proven to work beyond question, but currently are not practical given the alternatives, i.e. there is a more appropriate technology

Appropriate technology

Appropriate technology is an ideological movement originally articulated as "intermediate technology" by the economist Dr...

 for that purpose:

• General purpose robot
  Robot
  A robot is a mechanical or virtual intelligent agent that can perform tasks automatically or with guidance, typically by remote control. In practice a robot is usually an electro-mechanical machine that is guided by computer and electronic programming. Robots can be autonomous, semi-autonomous or...
  
  s (only economically feasible with rather drastic energy and material subsidy
  Energy economics
  Energy economics is a broad scientific subject area which includes topics related to supply and use of energy in societies. Due to diversity of issues and methods applied and shared with a number of academic disciplines, energy economics does not present itself as a self contained academic...
  
  , or in extremely hazardous applications that, arguably, no one should really be doing at all). However, note that specialized robots are widely used in industrial production.
• death ray
  Death ray
  The death ray or death beam was a theoretical particle beam or electromagnetic weapon of the 1920s through the 1930s that was claimed to have been invented independently by Nikola Tesla, Edwin R. Scott, Harry Grindell Matthews, and Graichen, as well as others...
  
   (there are easier methods of execution)
• jet pack
  Jet pack
  Jet pack, rocket belt, rocket pack, and similar names are various types of devices, usually worn on the back, that are propelled by jets of escaping gases so as to allow a single user to fly....
  
   (as yet impractical)
• antimatter weapon
  Antimatter weapon
  An antimatter weapon is a hypothetical device using antimatter as a power source, a propellant, or an explosive for a weapon. Antimatter weapons do not currently exist due to the cost of production and the limited technology available to produce and contain antimatter in sufficient quantities for...
  
   (with current technology, antimatter cannot be produced in sufficient quantities to be used as weapons)

Proposals for further development of these are thus more and more likely to be seen as fictional, misleading or amusing. Robot toys for instance have become popular. One could argue that the atomic bomb, given the consequences of its use, also belongs in this category.