March 3, 1999 – GNOME 1.0 was released by a team of Open Source developers, in large part, as a response to KDE. You see, KDE utilized the Qt UI toolkit, which many felt wasn't compatible with Free Software. In contrast to that, GNOME opted to utilize the Gtk toolkit, which was licensed under the LGPL. Beyond that, truth be told... GNOME didn't really bring many new ideas. But as time went on, the GNOME desktop continued to evolve and refine. Eventually, it managed to grab an incredibly large share of the Linux desktop market.
Fun Fact: GNOME stands for “GNU Network Object Model Environment.” And its logo is a foot. Who says developers don't make great marketers?