libsysactivity is a lightweight library that retrieves statistics of the system's activity in a portable and thread safe way. In each OS that it supports, it offers the same API for retrieving the activity of Hard disks, CPUs memory, Processes, Network interfaces, Memory, and Swaps.
The libstatgrab library provides an easy-to-use interface for accessing system statistics and information. Available statistics include CPU, Load, Memory, Swap, Disk I/O, and Network I/O. It was developed to work on Linux, FreeBSD, and Solaris. The package also includes two tools: saidar provides a curses-based interface for viewing live system statistics, and statgrab is a sysctl-like interface to the statistics.