Ask Slashdot: What's The Best Place To Suggest New Open Source Software?

dryriver writes:
Somebody I know has been searching up and down the internet for an open source software that can apply GPU pixel shaders (HLSL/GLSL/Cg/SweetFX) to a video and save the result out to a video file. He came up with nothing, so I said “Why not petition the open source community to create such a tool?” His reply was “Where exactly does one go to ask for a new open source software?”

So that is my question: Where on the internet can one best go to request that a new open source software tool that does not exist yet be developed? Or do open source tools only come into existence when someone — a coder — starts to build a software, opens the source, and invites other coders to join the fray?
This is a good place to discuss the general logistics of new open source projects — so leave your best answers in the comments. What’s the best place to suggest new open source software?

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