Blair O'Neil, co-owner of Integris Marketing, recently named Backpack the featured business resource at the Business II Business networking group's site.
Backpack now comes in a multi-user version that really makes this tool more like an powerful, on-demand, simple to use, Intranet for small business. You can create as many users as you like (price varies with number of users) and each user can have their own calendars, effectively creating an online sharable calendaring system. The newsroom feature is a like an activity dashboard that also keeps group messaging tidy...I really think it’s killer when combined with Basecamp. If you use multiple offerings from 37signals, one tip I would suggest is to get an OpenID and use it to log in to your accounts and then you will have the ability to jump back and forth to all of your accounts from a simple dashboard interface.