AbiWord, Blender, FileZilla, GIMP, LibreOffice (formerly known as OpenOffice, formerly known as Star Office), Opera, PuTTY, Seamonkey (formerly known as Mozilla Suit), Stellarium, Thunderbird, WinSCP<p>KDE and Gnome probably have some old running apps too. There are many long-running open source desktop-apps I think, because there is no economical stress for its development.<p>In the commercial section I could name Directory Opus, DEVONthink, Maple, Mathematica, Pegasus Mail, The Bat!, Tinderbox