NihAV is a research multimedia framework built on not invented here syndrome and licensed under GNU Affero General Public License 3.0 (relicensing to other free licenses available on request).
You can get the source code for it at git://git.nihav.org/nihav.git and source code for the tools at git://git.nihav.org/nihav-encoder.git, git://git.nihav.org/nihav-player.git and git://git.nihav.org/nihav-tool.git.
You can read more about NihAV here and also read an architecture overview and crates contents overview.
And here is a short guide on how to encode VP6 with NihAV.