My company (Matterport, YC Winter '12) uses it to store metadata about 3d models. I really don't have that much to say about it because it's not my primary area of focus, and besides that, has been extremely reliable and hands-off, administration-wise. I particularly love that you can change redundancy modes on the fly, for example those listed here[1], and FDB will automatically re-arrange data to your liking, all without downtime. It handles offline/missing or replacing nodes quite well, and I credit my coworker's great efforts to make it work on top of Kubernetes for making our lives so much easier.

1: https://apple.github.io/foundationdb/configuration.html#choo...