fwiw, Spine is made using libgdx [1], which is open source. The various stretch-goal animation runtimes are also available [2] on Github.

AFAIK the team behind both libgdx and Spine are quite good at giving back to the community. After libgdx they quit their day jobs and went full-time as Esoteric Software [3] and did an excellent job following through with Spine's two kickstarters.

I think this is very relevant to HN not only because of the guys' open source contributions but also their entrepreneurial history (success?).

[1] https://github.com/libgdx/libgdx [2] https://github.com/EsotericSoftware/spine-runtimes [3] http://esotericsoftware.com/

(I'm not affiliated with ES but was a backer of Spine and am a user of libgdx)