KDE, a mature functional graphical user interface (GUI) for Linux and UNIX, is widely used, but is not favored by enterprise Linux vendors, who appear to prefer the GNOME environment. The GNOME environment has been selected for Sun Microsystems' Solaris and its Java Desktop System (JDS). Both KDE and GNOME have their strengths, and competition between KDE and GNOME is beneficial for users. The most often described problem with KDE is the way the Qt framework is built. Trolltech, the builder of Qt, licenses it and distributes it under a dual-license scheme. Qt X11 is free for open-source projects, but a per-developer license is required for creation of proprietary software. For this reason, Bruce Perens, an open source advocate, decided to exclude KDE in favor of GNOME from a soon-to- be-available enterprise-targeted, community-led UserLinux distribution. GNOME, says Perens, is built on a framework called Gtk+ that can be used to create free and proprietary software without royalties. However, Qt is also one of KDE's most important assets, since it provides good development tools and runs on more platforms than Gtk., including Windows, Linux/UNIX, Mac OS X, and embedded Linux. KDE also focuses on extra functions and configurability, and its Konqueror file manager does much more than GNOME Nautilus. However, Konqueror has a confusing number of buttons and preferences screens. In spite of their differences, however, users will benefit from having a choice between KDE and GNOME.