I'd say not even just FOSS, but indie developers can get a lot of value out of Lazarus and Free Pascal. It is by far the easiest way I've found to create a quick cross platform desktop application. When I say quick, I mean quick to develop, quick to compile, and it produces native binaries (using the native toolkit!) that are quick to run and use less memory than the alternatives.
The biggest weakness is that it's not great for iOS and Android.
To code some FOSS stuff, enjoy a fast compiler toolchain and RAD experience for GUI applications, worth a try.