LTSP - The Linux Terminal Server Project adds thin-client support to Linux servers.
Firebase - Firebase is a cloud service designed to power real-time, collaborative applications for mobile and web.
Thinstation - Thinstation is a basic and small, yet very powerful, open source thin client operating system...
restdb.io - restdb.io lets you create databases and REST APIs quickly. Development databases are free. Powerful web-based and mobile-friendly data management.
Nakama - Nakama is an open-source distributed social and realtime server for games and apps.
RemoteStorage - An open protocol for per-user storage OWN YOUR DATA