All the software I write is mainly using free tools, engines and programming libraries, except blitz3D which I have a license for.
I have used / and still use .. many of the following:
Bloodshed Dev C++, VC6, CodeBlocks, MinGW, SDL, Java
Free 3D Engines: Ogre, Irrlicht, Panda3D, CrystalSpace, Jolt3D, RenPy, Allegro, Unity, 3Drad. Shiva PLE, Esperient ..
Free Libraries: TokaMak, Bolt, Plib, Osalp, irrKlang, ClanLib
Free modeling tools: Blender, TrueSpace, gMax, Sketchup, Wings3D, Anim8or, CharacterFx
Free paint / image tools: The Gimp, Paint.net, IrfanView
Free texturing tools: Blacksmith3D, Gimp, SpriteCraft
Free Terrain Generator & lightmappers: L3DT, Terragen, Giles
Free sound tools: Audacity ... and others