As part of my de-Googling, I've been meaning to start migrating my projects away from Firebase, which has been hard because it's just so damn useful. But I've started building my own open-source BaaS / backendless / no-backend alternative called Direbase. So far, it's extremely sparse — only supporting username / password authentication and simple databasing — and it's almost certainly not very secure. (Seriously. I don't know what I'm doing.) But it's been so much fun to make, and even more fun to see in action. The databasing relies on FileDB, an open-source, dependency-free database solution for Node that I just built as well.
I've migrated my Notes app over to it, though I've left the old Firebase version up for public consumption (since I use it as part of my portfolio). If I ever get around to tightening up security on Direbase, I may point all of my apps to it.
If you decide you want to try it out, let me know! And also, don't run anything mission-critical on it! Enjoy!