From README.md ( https://github.com/threema-ch/threema-android ):

> This source code repository will be updated for every public non-beta release. There will be one commit per released version. [...] For the time being, we do not accept contributions via GitHub. [...] To report bugs and request new features, please contact the Threema support team through threema.ch/support.

Commits are useless (one commit per release), issue tracker on GitHub is disabled, contributions not public, no public discussions. I like Threema and appreciate them open sourcing their apps, but this is not what I call open source development. I really hope they will reconsider this. Both Threema and the community could benefit from this, but dumping the source code here and then isn't going to cut it when the competition is meanwhile doing real open source development. But at least we have reproducible builds now, this is still a great step forward.