When it comes to online project management services, so many people will turn to 37 Signal's "Basecamp". Arguably one of the most feature rich.Freedcamp so awesome isn't JUST the fact that it's completely free, but the fact that it offers so much, and feels so smooth. Just logging in is fast and simple. You can plug in using your Facebook account and BAM you're done.
You have multiple projects, to-do lists, groups, time tracking, discussion boards, file sharing, instant messaging (using Meebo) and even invoicing.
Adding information into Freedcamp is simple. Create a new project, add a task (to-do) and done. You can quickly and easily add and drag your to-do list items, assign someone to it, set a schedule .. it's so robust it's hard to believe it IS free!
If you're looking for something to replace Basecamp, this is the online service for you. In my opinion, Freedcamp is the Basecamp killer.