Over the past few weeks I’ve been working on a version of AgileAgenda (project scheduling app) that tightly works with Basecamp. Previously, we had a fairly poor synchronization between the two. But now AgileAgenda directly reads and writes to your Basecamp project, so it’s a lot cleaner to use. So if you've ever wanted Gantt Charts in Basecamp, you might want to take a look.
It’s still a work in progress, but if you’d like to take a look, I’d really appreciate any feedback: http://agileagenda.com/basecamp/
If you want to just see a glimpse of it, there’s a quick video: http://agileagenda.com/basecamp/video.html
One neat thing I’m doing that other Basecamp integrated apps might benefit from; I need to store quite a bit of information that Basecamp doesn’t handle natively. Things like associating a duration to a todo item or an estimated start/end date. To do that I’m storing it to an XML snippet, base 64 encoding it, and putting it into a private message within an invisible span tag. In the message I throw in some status info and attach a document, so the message is valuable to more than just the app. Screenshot of that:
Again, I would appreciate any feedback, trying to make something within a bubble of how I use it can be tough.
Also, as part of this, I've been working up a pretty comprehensive AS3 library to deal with the Basecamp API. I'm not sure what I want to do with that yet. Perhaps an open source thing, maybe a for-pay license (maybe even dual-license). Would anyone be interested in something like that?