When 37Signals created Basecamp, they filled a huge void in the project management market: the world was full of people who needed to actually manage projects and communicate, rather than learning the black magic of project management and its complex terminology. Free alternatives to Basecamp took a long time to develop: ActiveCollab was released around 2006, a good 2 years after Basecamp. Right now, the most established free alternatives are Project Pier and FengOffice. There are tons of non-free alternatives to Basecamp out there. They are all page-reload applications that mimic Basecamp's interface quite closely. Amongst the non-free ones, there is one I'd like to see as free software: Apollo. More about Apollo later.