For me with GameStudio

- Blender
- GIMP
- Code::Blocks / Visual Studio(Or another C/C++ IDE)
- SMEE
- Sphere
- DEX Soft

But for GameDev in general:
- Modelling, e.g. Blender
- IDE, e.g. Code::Blocks
- Compiler, e.g. MinGW/gcc
- Intarwab, e.g. Google
- Image handling, e.g.GIMP
- Engine, e.g. GameStudio / AGE
- Audio handling, e.g. Reason

"Yesterday was once today's tomorrow."