As far as I'm aware, this does not belong on StackOverflow, but where does it belong to? Is there a place in the StackExchange-community for this kind of requests?
I guess it would be easiest to just redirect people to SourceForge or similar, but since I can't really imagine how you could reformat the question to have that answer, without it being a shopping question, there's probably not much to do to prevent them from happening, other than removing or closing the questions.
Agreed with other answerers that this doesn't belong on StackOverflow, but I would think a better close reason would have been Not Constructive:
As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or specific expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, see the FAQ for guidance.
What project should I contribute to clearly fits into the "questions likely to solicit debate" category in my book.