I experimented with ObjectBox a bit, but I decided against using it because it isn't open source. The language wrappers are apache2 but the core library is only provided as a binary blob. I think this is bad because you can't inspect how it works, fix bugs, port it to new archs, integrate it fully into your build system, etc. Also, every cursor operation must call into their function entry points (as opposed to being inlined in your code for example).

Instead, I've been working on my own library which also uses LMDB and flatbuffers. It's C++ only and still a WIP, but in case anyone else is interested, it's here: https://github.com/hoytech/rasgueadb

Thanks for sharing your experience with it, makes me wary.