Basecamp is a new and very promising online service offering web-based project management for everybody. The service relies on open standards like RSS and iCalendar to allow progress tracking with a RSS reader and an iCalendar compatible calendar application like iCal. The user interface is very clean and slim (CSS-based formatting only) and makes clever use of JavaScript to enhance the user experience (did I say that?).
While the service is not free in general, everybody can set up accounts for free and run a single project with multiple partners at no cost. If you want to have more than one project at the same time means paying a monthly fee.
Given the current state of glorious absence of anything that could be called an acceptable solution for project management on the Mac this approach is really refreshing. I like the combination of web-based modification of project data and the option of having customized tools for tracking the progress (like using NetNewsWire and iCal on the Mac). Hopefully, posting to the weblogs will come with a XML-RPC interface for weblog clients soon.