Here you will find some (hopefully) useful links

Boson at SourceForge Boson uses SourceForge.net's services
The Boson handbook
KDE homepage Boson uses KDE
Trolltech (creators of QT) Boson also uses Qt
freehackers.org Other free software
SF.net SourceForge.net

Stratagus an real-time strategy gaming engine, successor of FreeCraft
Project Inferno an Open Source Real Time Strategy Engine
FreeCNC Command & Conquer clone for Unices
ASC Turn based strategy game
Vegastrike Open Source 3D space simulator. Not really related to boson (no RTS or so), but I consider this very important, so...
Freeciv Strategy game. Neither real time nor OpenGL, but it is playable and since there aren't so many "big" free games that are playable it is listed here.
Glest Real time 3D strategy game for windows.
TA: Spring Real time 3D strategy game for windows. A linux port is being worked on.
ORTS Real time 3D strategy game environment. ORTS is primarily meant for studying real-time AI problems.

PLIB A OpenGL widget/font/scenegraph library. Also includes a library for sound and network (and more).
SDL Probably the most important unix game library
Crystal Space Portable 3D Game Development Kit
Allegro A game programming library for C/C++ developers
Gamasutra A LOT of high quality articles related to game programming. Usually you need to search in the archives a while to find what you can use.
Amits Game Programming Information You can find answers to general questions on game programming here, but more important is probably the collection of links on AI and pathfinding.
Free game arts Collection of textures, models and so on. Not all are free (as in speech)!
Gamedev.net Many very useful articles and tutorials here