Well, I can't honestly say it's better than JumpBox -- as I've never tried them. I've fondly oogled their website for some time now -- WISHING I had a reason to pay for their service, but could never justify the price.
I'm so happy to have found Turnkey! This is exactly what I've been looking for. I installed the Joomla appliance -- and it all went without a hitch.
I can't wait for your Tomcat and JBoss appliances to be released. I'm a software developer -- but I do 99% of my development on windows and then just deploy to linux/unix servers. I've played with linux off and on for years -- and have watched the appliance market start to take off. I'm a big fan of the idea.
Anyway -- if I can be of service, I'd be glad to help -- even if it's only to test.
Another appliance to consider is one with Oracle XE and Sql Developer installed. I actually found one by a book author and like it very much. It would be even better with the Turnkey special touches. Oracle XE is the free Oracle (as in beer) and it's very useful for developers in corporate environments that are using oracle.