Crucible is geared for kernel-level testing, particularly for networking tests (NFS, Samba, etc.) which require orchestrating multiple machines working in conjunction on a given test. It also supports reimaging test machines between test runs, upgrading the kernel, and automatic power cycling. (Assuming you have the hardware to support these things!)

Crucible was originally derived from the Samba Build Farm scripts. It was created because while there are a lot of automated test harness out there, none were found that could both do kernel booting and allow for testing across multiple machines. The Samba build farm was selected as a starting point because the code was simple and relatively clear. It was developed at the Open Source Development Labs (see http://crucible.sourceforge.net/).