For BetaCopter go to https://github.com/olliw42/ardupilot/branches, and pick a BetaCopter branch.
For licenses, terms of usage, acknolwedgments, sources, and so on, go to the same link and pick a BetaCopter branch.
Latest 'u' version:
betacopter 3.6.1 v015u this version is derived from Copter 3.6.1
Latest 's' version:
betacopter 3.6.0 v013s this version is derived from Copter 3.6.0
The 'u' version has ALL UC4H and STorM32 related additions ('u' for UC4H); the 's' version has all STorM32 related additions, but misses the UAVCAN/UC4H realted stuff ('s' for serial).
For your convenience, some binaries are also hosted here for download:
Please see http://www.olliw.eu/storm32bgc-wiki/STorM32-ArduPilot for information on the usage and features of BetaCopter.