Sysinfo is a linux daemon written purely in Java that exposes OS info and metrics via a REST API.
After chasing around APIs and hacks around system stats, I finally wrote my own System statistics and info daemon that is written purely in Java.
Why REST? Push is not always the best solution to get system metrics, with this you can query metrics in real-time directly off the host.
Sysinfo has been written with cloud and high performance applications in mind and thus adds negligible overhead (in my tests, consumes less CPU than htop)
The license of this project is Apache 2.0.