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.
The API is a RESTful with both JSON and XML support. It plans to add OAuth support at some point, but the current authentication mechanism is Basic Authentication. As this is through HTTP rather than HHTPS, it's not the most secure authentication method, so be warned. I look forward to them adding OAuth in the future.
This API could be used to make a client for mobile devices, or integrate the service with other web services. Personally, I think a Facebook app would be a great use of it, as Facebook integration works well with what is essentially a social service. This would allow users to find more friends that also use Dive.io, as well as help get the word out to other divers about it.