Basecamp is a good product but only if you share its "opinion" on workflow and design. Obviously 37Signals has done well by sticking to a minimal set of features and catering to a very specific audience.
We are of the mindset that software should fit the way you work, not necessarily the other way around. We're building a Force.com-like platform that allows you to create custom business workflow apps in minutes to handle not just tasks, but also lightweight crm, recruiting, and other business functions involving a relatively defined process. We provide a fast UI to access these records, so all you do is specify the schema and callbacks.
We're still in beta, but happy to release some invites and work with members of the HN community -- http://www.devcomb.com