We keep track of projects using a private wiki. Here's most of its main page:
As you can see, we have tasks divided up into separate todo list pages. That way, anyone who's good at, say, 3D modeling can browse that todo list and pick a project they'd like to work on. I expect that we'll add a Graphics Todo List and a Level Design Todo List, as well.
"Giv[ing] [tasks] to a relevant member to try to make" wouldn't work, because it implies some sort of management/workforce structure. Quite the opposite; we make almost all nontrivial decisions by discussion. (Infrequently, when we really can't agree on something, we'll vote.). As such, there's no reason why anyone could "give" anyone else specific projects to do.
The general outline of the game, as well as plans for specific levels, is kept on the World List page. Things that require extended discussion, such as the plot and world map layout, are discussed on a private board.
The "Todo" page near the bottom of the screenshot is our single, unified todo list that we used before we switched to maintaining separate ones (which works much better).
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