xosview is the classic system monitoring tool, for Linux, *BSD, HP-UX, IRIX, Solaris and GNU.
As the original project appears to be dead for some time, I created a new repository — starting with the most recent code from CVS, patches from the Debian package, and adding new patches to fix some of the bugs. Development has continued, and this is now the upstream source for several Linux distributions.
The display can be customised and there are some screenshots contributed by users. The old users mailing list is hosted on Sourceforge; please use this for related discussion.
(There was previously a devel mailing list but this appears to have been deleted and it isn't clear the reson why, but I was not able to find the maintainer of these lists.)
The most recent release is xosview 1.16 (8th November 2013)
The source code repository is hosted on Github:
$ git clone git://github.com/hills/xosview.git
Licensing terms are varied, and are contained in the source code.