Tally4.com is a web application that helps you put your Foursquare checkins to work.

Whether it's working out, eating local or volunteering, you're out-and-about for a purpose. Foursquare records these checkins -- it lets your friends know when you arrive, and can give you coupons. It's great for shopping, but what about for goals? 

That's where Tally4 comes in.  

Tell the app what you care about, and Tally4 shows your pertinent checkins. See at a glance when you've worked out, and when you, um, may have slacked.

Are your friends interested in the same stuff? Tally4 keeps score, so you can race them to your goals.

It's perfect for fitness, comparing restaurant notes or tracking club attendance.

Tally4 was conceived and built by el-studio.com, using the Foursquare API.

Aboutfoursquare.com's review sums it up: 

Tally4 is yet another interesting way to use foursquare’s checkin data.