Lately at Beeminder we’ve been using Trello for just about everything. We use it to stage blog posts and track bugs and new features on the Beeminder API and website. The Beeminder iPhone and Android apps each have their own board too.
“We automatically track the number of cards in your Done list.”
Moving a card into the Done list feels pretty awesome. So in order to feel more awesome more often, we figured we’d beemind the number of cards in that list! But it’s pretty easy to forget to update your Beeminder graph every time you move a card into the Done pile. For many kinds of goals the Beeminder email bot or SMS bot solves the forgetfulness problem nicely: just reply to the bot with your number every day. But that would be annoying for Trello since you’d have to go and count the number of cards.
Enter the Trello API. We’ve set up a new goal type that automatically tracks the number of cards you’ve moved into one (or more) of your Trello lists. You can set one up just by pasting a link to the Trello board you want to track. If your board is private, you’ll be prompted to let Beeminder access your Trello account with the typical OAuth goodness. 
Then just use Trello like you normally do. Move a card into one of the lists you chose and you’ll see the data point appear on your graph, usually within 10-15 minutes (we don’t want to overload Joel’s servers!). UPDATE: Beeminder fetches your data less often than that now but you now can just hit the refresh button on your graph page if you want it to fetch your latest Trello count Right Now.
I’ve set up Beeminder goals that are tracking how many cards we finish on our website board as well as our API board. . So I’m on the hook for $10 if we start slacking. Now you can be on the hook too (for your own boards, that is):
 We never see your password and we’ll never look at anything except the number of cards on the list(s) you specify.
 These Trello boards are all completely open to the public, and we’ve tried our best to let anyone contribute. It seems like Trello requires that you be manually added as a contributor before you can create cards, but if you ask us we’ll definitely add you. And if someone at Trello is reading this, we’d love a promiscuous mode for boards that lets anyone at all contribute to them!