JavaSysMon is designed to provide an OS-independent way to get live system information, such as CPU and memory usage, and manage processes, distributed as a single jar file. It is written in C and Java. However the native binaries are hidden away inside the jar, so you never need to worry about them.
The main API is to be found in {@link com.jezhumble.javasysmon.JavaSysMon}, so start there.
JavaSysMon is licensed according to the terms of the NetBSD (2-line BSD) license.