Browsershots 21 May
Browsershots is a new open source project offering web page testing in multiple browsers, just like SiteVista will. At time of writing it supports six different browsers, all running on Linux. There's currently a 49 hour wait (!) to receive your screen captures, but I assume this will drop as they get more volunteers donating their PCs to the cause.
Looks like an interesting project to keep an eye on as it develops further.