GDebi is a tool that can install .deb

Deb (file format)

deb is the extension of the Debian software package format and the most often used name for such binary packages. Like the "Deb" part of the term Debian, it originates from the name of Debra, erstwhile girlfriend and now ex-wife of Debian's founder Ian Murdock.Debian packages are also used in...

 packages. It is available with a graphical interface, but also has a command line option. It is updated by using Update Manager

Update Manager

Update Manager is a program that updates all installed software and their associated packages, with important software updates for security or recommended patches. It also informs users when updates are available, listing them in alphabetical orders so that users can choose which updates to...

.
It was included by default in Ubuntu

Ubuntu (operating system)

Ubuntu is a computer operating system based on the Debian Linux distribution and distributed as free and open source software. It is named after the Southern African philosophy of Ubuntu...

, until Ubuntu 10.10. In Ubuntu 10.10 Maverick Meerkat, GDebi was replaced by the Ubuntu Software Center

Ubuntu Software Center

Ubuntu Software Center is a computer program for browsing, installing and removing software on the Ubuntu operating system. Based upon the GNOME application, gnome-app-install, which is similar in function and appearance, it serves as a GTK+ graphical user interface front-end to the Advanced...

. In Ubuntu 11.10, Ubuntu Software Center includes Gdebi functionality to increase the speed of .deb files installation.

Technology

GDebi can install local .deb packages with automatic dependency resolution (it automatically downloads and installs the required packages). While Gdebi is no longer the default program to handle .deb packages in Ubuntu 10.10 and above, Gdebi is considerably faster than Ubuntu Software Center.