Over a couple of weekends, mostly as an exercise in learning a new language (scala) / framework (lift) two friends of mine and I came up with: demo.udunit.com.

In a nutshell it is:
UdunIt (pronounced you-done-it, as in whodunit): A fun way to share, boast about and track your progress towards major life accomplishments, as well as discover new ones to take on! People love grouping things into lists — it's a natural human tendency: The Four-thousand Foot Mountains of New Hampshire, California Micro-brews, Best Restaurants in Austin, TX. We want to motivate people to take on these challenges, to get out and do something. Udunit will bring social and gaming aspects to these accomplishment lists, building on people’s desire to share their accomplishments as well as their competitive natures.

Based on Foursquare's engineering blog (which has lots of good technical information about how they do things) we decided to give Lift a try and learn Scala along the way! Did we like it? Yes and no. I am intellectually attracted to functional programming and enjoyed Scala in that regard. However, the type system gave us some headaches (seems to be a common comment), and we found that in general there was a tendency in the community toward less than readable code. Lift's documentation left a lot to be desired and was often behind the current "best" way of doing things.

It was fun+frustrating to play with and our next project won't be using Lift/Scala, but I've been playing with Opa and am excited to try that for a project!