Features:

- Drag & drop interface
- Backgrounds, sprites & images
- Animated graphics
- Rotate sprites
- Internal image editor
- Modify resources at run-time - sprites, backgrounds, paths etc.
- Particle effects
- 3D graphics
- Full-screen anti-aliasing
- 3D hardware acceleration
- Off-screen surfaces - for rendering dynamic textures
- Interstitial screens - loading screens, videos
- Font control
- Advanced text drawing - rotation etc.
- Sound effects & music
- Audio processing effects - reverb, delay etc.
- 3D sound
- Built-in data structures - stacks, lists, dictionaries, queues etc.
- Paths and timelines
- AI pathfinding
- Internal code editor - with user-definable syntax colouring
- GameMaker Language (GML) - highly flexible scripting language
- Extensions - using custom external DLLs
- Packaged with images and sounds - freeware samples
- Auto-updater - for updates and bug fixes
- Create executables
- GameMaker watermark on executables

Requirements:
Windows XP, Windows Vista or Windows 7
DirectX 8-compatible graphics card with at least 32MB of video memory
Pentium or equivalent processor
DirectX 8-compatible sound card
156MB of memory or greater
800x600 or greater screen resolution with 16-bit or 32-bit colors

Home:
http://www.yoyogames.com/gamemaker/windows