- Anything requiring attribution (e.g. CC-BY, but also BSD, …)
- Anything putting conditions on the right to “use, display and perform” the work and, worse, “reproduce” (all Copyleft [maybe minus GPL])
- Anything requiring integrity of the author’s source (e.g. LPPL)
There's a fair bit more detail on the post, but that's the gist of it.
The concerns relate to section D of the new ToS, which is here:
https://help.github.com/articles/github-terms-of-service/#d-...