There's Simperium (disclaimer: I was a cofounder, YC S10). It's powering optimistic sync for millions of users of Simplenote and WordPress.com. It has JavaScript[1] and Python[2] libs, but its strength is iOS[3] and Android[4].
The team focused on internal use though, and hasn't had a chance to open source the backend and flesh out the web side of things. I hope they get a chance to do another iteration (we were bought by Automattic/WordPress and I'm no longer there).
The team focused on internal use though, and hasn't had a chance to open source the backend and flesh out the web side of things. I hope they get a chance to do another iteration (we were bought by Automattic/WordPress and I'm no longer there).
[1] https://github.com/Simperium/simperium-ios
[2] https://github.com/Simperium/simperium-android
[3] https://github.com/Simperium/simperium-js
[4] https://github.com/Simperium/simperium-python