Project management tools are, of course, the ultimate expression of social productivity. And few project management services get quite as social as . The free version of Huddle lets you share one workspace with your colleagues, giving you a shared calendar, the ability to assign and track tasks, and 100MB of storage space for documents and files. For $25 per month, you can upgrade the storage to 2GB and add conferencing capabilities. (You can find a few higher levels of service beyond that, too.)

Of course, getting everyone on your team to start using yet another Web service can be challenging. But if that service connects to something they're already logging in to--such as LinkedIn--then you're halfway there. Huddle lets you link your account to LinkedIn, and then gives you easy tools for inviting your connections to join your workspaces so that you can assign them duties and check their progress without even going to the Huddle site.

Like Huddle, offers robust project management tools that connect to LinkedIn. What it adds to the mix is the ability to share Google Docs and Google Calendar information, plus a Gmail gadget that puts your Manymoon account right into your inbox. For groups that are already using Google Apps to share information, this is a great feature.

A basic Manymoon account is free; premium accounts (ranging from $19 to $49 per month) add cool project reports, custom page designs, and advanced administrative features.