We recently open sourced Keywhiz, a piece of infrastructure to manage and distribute secrets across services.
A really neat thing about Keywhiz is that the client API uses FUSE. FUSE makes it easy to manage files which contain secrets (think database, web server configs or API keys) without having to actually persist the data on disks.
In addition, the code has been battle tested for over 3+ years of use at scale.
The server is written in Java and the client filesystem is written in Go.