We started by building an application to support choirs and choruses because singing is our passion! But lots of other groups could benefit from a tool like Groupanizer for all the same reasons - it can be made to really understand the problems and therefore give much more lift than any free or general-purpose tool.
Just to get the ball rolling, it seems that service clubs are a good candidate for a Groupanizer solution. Right now we are doing a trial with an Elks lodge. They particularly like the project management module, since it turns out they have standard projects that need to be run.
What other group types do you think might be well served by a Groupanizer solution?