Lumix Engine - Open source 3D game designer and engine written in C++.
Smooze - Smooze animates your scroll and adds functionality to your non-Apple mouse (scroll-wheel mouse).
Grit Game Engine - The Grit Game Engine is an MIT-Licensed Open Source Game Engine that is highly scriptable via Lua.
Smart Scroll - Smart Scroll makes scrolling smoother, faster and more comfortable:
MOS - Lightweight game engine.
Caldis MOS - A little job for your mouse.