Webform for cumulative signup sheet?

Has anyone ever adapted Webform or used its API to create a cumulative signup sheet for use by multiple people? For instance, one might have a sheet of meeting times, with one slot per meeting time. A user fills in one slot. When the next user sees the form, that slot remains filled in, and the new user will need to choose one of the remaining empty slots. Or one might have a signup for a potluck, with multiple slots. Each person enters their name and what they're bringing. Later users can see what the previous people wrote.

In my case, the users are cooperative, so all the slots can remain editable even if they are filled in. But one must handle the race condition of two users trying to fill in the same slot at the same time.