Our Eggplant tool can test software on any operating system for which a VNC server is available. The trick then for testing software on these platforms is whether there is a VNC server that will provide access. Unix, and I believe Alpha, shouldn't be a problem. The AS400 and mainframe operating systems are less certain. However, if you access those systems through terminal software running on a PC, though, then the problem is solved, as there are plenty of PC VNC servers.
Feel free to contact our sales or support staff if you'd like to explore this possibility further.
Doug Simons, Principal Developer
TestPlant, makers of eggPlant, the Cross-Platform GUI Testing Tool http://www.testplant.com
We use TestComplete ( http://www.testcomplete.com ) by AutomatedQA and have had great results. Software Planner ( http://www.SoftwarePlanner.com ) also has a keyword driven testing framework that works with TestComplete so that you can create automated test cases using keywords rather than scripting -- this saves lots of time.