(formerly RealStudio) is a visual basic-like language except that it's realy OOP (has nice things like interfaces and delegates for example) that compiles to programs that use native GUI widgets on Windows, Mac, and Linux. No, it's not as powerful as C/C++, but it's a lot easier/quicker.
It's biggest weakness (IMHO) is that it's developed by a small, private firm that seems resource constrained. This leads to some releases having real issues and it taking some time for those issues to be sorted. That can mostly be mitigated by only updating once you know the current version is quirk-free.
Xojo also has a decent plugin architecture/SDK so you can write "heavier things" in C if you need to. It also handles decalres against C libs pretty well.
Xojo's definitely worth taking a look at (again IMHO) if you really need to build cross-platform software (small business applications for example).