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.

Also part of the package are two tools; saidar provides a curses-based
interface to viewing live system statistics, and statgrab is a
sysctl-like interface to the statistics.

WWW: http://www.i-scream.org/libstatgrab/