CrossBridge is the open-source version of Adobe FlasCC (formerly the Alchemy project). It provides a complete C/C++ development environment for targeting the Adobe Flash Runtime.
crossbridge.io

Features:

• LLVM-GCC 4.2 compiler with Flash backend
• GDB debugger that debugs your code while running in the Flash Player
• SWIG backend that auto-generates inter-operability code, allowing you to build Flash libraries (SWCs) that wrap C/C++ libs
• Multi-threading based on POSIX Threads

Community:

• forum
• irc channel #crossbridge irc.freenode.net

Download:

• Windows release
• Mac OS X release
• All the releases on the SourceForge Project

Examples:

• NeverBall
• GLSDL
• StarlingFilters
• QREncode
• LUA
• LUA with Starling
• LiquidFun
• OpenGL