InsaneJournal

How it works:

When you submit this form, your request will be added to the list of open requests. You'll get an email with a link in it that will allow you to change your request up until someone "claims" it. Once someone has claimed your request, you won't be able to make any changes. When they've finished writing your ficlet, you'll get an email with a link to where they've posted it.

You get to make one request for free. After that, you can to contribute to the jar by writing ficlets for other people. Every ficlet you write and send along gives you the option of adding another request, and thus the cycle of ficlet gifting continues.