Qt (pronounced as /ˈkjuːt/ "cute") is a cross-platform application framework that is widely used for developing application software with a graphical user interface (GUI) (in which cases Qt is classified as a widget toolkit), and also used for developing non-GUI programs such as command-line tools and consoles for servers. 
In Gentoo, the Qt ebuilds and related packages are maintained by a dedicated team which is a subproject of the Gentoo Desktop project. This team also maintains the official qt overlay. They are very open to user contributions and volunteers who want to become new developers.
Installing the Qt libraries
Most users will not need to install the Qt libraries intentionally, but can just let them be pulled in as dependencies of the applications they want to use. For those who want the complete set (e.g. for software development purposes), there is an x11-libs/qt-meta ebuild, and there are sets in the overlay.
If you want to change the appearance of applications using the Qt toolkit you can use the Qt Configuration tool (
qtconfig). It's an easy way to set themes, fonts and more advanced settings.
Qt based desktop environments
There are currently three Qt based desktop environments available in Gentoo. The most well-known and best developed one is KDE. More recently there are also two more "light-weight" DE in development: Razor-qt and LXQt. These can be complemented with applications from the desktop applications list.
Frequently Asked Questions
Please see the Qt/FAQ page.