Here's a screenshot of CheckItOut running on Haiku version 22479.

CheckItOut on Haiku

As you can see, the application appears to look the business, with a few font issues and the lack of transparency on the picture, but unforuntately, it's all downhill from here. Instead of the app invoking the CVS command, the Terminal pops up and nothing happens.

As Haiku is still pre-alpha, these things can be expected. I'll look into it some more and will in due course post on Haiku's bugtracker.