Dive.io is an online social service where SCUBA divers can post information about dives they have completed and places they dive. Other users can then browse dive records and see other user's opinions on the dives. Dive.io also provides a RESTful API allowing developers to create their own applications and websites for accessing Dive.io data and uploading/retrieving dive records.
With the holiday weekend coming up in the U.S., avid divers may be making their way to their favorite spots. Dive.io is a web service designed for divers, so they can log their dives, share their favorite dive spots, and meet fellow divers. It's very specific, but it does its task quite well. It also has a nice API, allowing for integration of the service into, well, anything at all.