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From 37signals. Basecamp is a unique project collaboration tool. Projects don't fail from a lack of charts, graphs, or reports, they fail from a lack of communication and collaboration. Basecamp makes it simple to communicate and collaborate on projects. The Basecamp API is implemented as vanilla XML over HTTP.
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There are no source code libraries or how-to links for Basecamp. If you know one why not add it?
It may be good for communication, but for managing my projects I chose Wrike http://www.wrike.com/ after reading this article http://www.pcworld.com/businesscenter/article/134816/project_management_lite_basecamp_and_wrike.html
I love it. We use it daily to manage the development of our software. Go 37signals!