Rietveld is a web-based collaborative code review tool for Subversion written by Guido van Rossum

Guido van Rossum

Guido van Rossum is a Dutch computer programmer who is best known as the author of the Python programming language. In the Python community, Van Rossum is known as a "Benevolent Dictator For Life" , meaning that he continues to oversee the Python development process, making decisions where necessary...

 to run on Google's

Google

Google Inc. is an American multinational public corporation invested in Internet search, cloud computing, and advertising technologies. Google hosts and develops a number of Internet-based services and products, and generates profit primarily from advertising through its AdWords program...

 cloud service

Google App Engine

Google App Engine is a platform as a service cloud computing platform for developing and hosting web applications in Google-managed data centers. It virtualizes applications across multiple servers,...

. Guido based Rietveld on the experience he had writing Mondrian. Mondrian is a proprietary application used internally by Google to review their code.

Gerrit

Gerrit (software)

Gerrit is a free, web-based collaborative code review tool that integrates with Git. It has been developed at Google by Shawn Pearce for the development of the Android project....

is a fork

Fork (software development)

In software engineering, a project fork happens when developers take a legal copy of source code from one software package and start independent development on it, creating a distinct piece of software...

 of Rietveld started because ACL

Access control list

An access control list , with respect to a computer file system, is a list of permissions attached to an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject...

patches wouldn't get integrated into Rietveld.