37Signals.com - Maker of collaboration tools

8apps.com - A mixture of social network and productivity applications.

BlueTie.com - Online collaboration

Businessitonline.com - Centralized cash flow, documents, calendars

CentralDesktop.com - A full work suite for project teams including spreadsheets, file sharing, calendar and more.

Colligo.com - Allows you to work on projects off-line and then sync them when you can login.

ConceptShare.com - Share concept designs and allow invited workers to mark-up, comment, and give feedback.

Confluence - An enterprise-class wiki with features such as PDF exporting.

ContactOffice.com - groups to share documents and more

Coventi.com - Upload your documents, share, allow others to highlight portions or edit.

Copperproject.com - Share projects, tasks, documents and timelines

CrossLoop.com - collaborative work and transfer of files.

Eloops.com - Share files, calenders, projects,

Foldera.com - Allows for communication over projects, and centralizes work

Glide - group meetings

Google Docs & Spreadsheets - collaborative documents and spreadsheets.

GroupSharp.com - share lists, databases, file sharing, and wikis

Huddle.net - collaborative work in the fields of PR, advertising, marketing, design and more.

Instacoll.com - real-time sharing of documents

Joyent.com - collaborative software and backup services

Longjump.com - standard collaboration,

Mindquarry.com - Work on projects online or off-line

musical collaboration site where you can jam with other musicians. Jam sessions can be broadcast live

Become a beta tester now!

Near-Time.net - Build wikis, blogs,create documents

Nexo.com - Share files and notes

Octopz.com - a wide range of documents including video, audio, and flash animations.

OpenTeams.com - create cPages of your project.

QuickBase.com - A collaborative tool

PlanHQ.com - Specifically for groups working on business plans.

ProjectSpaces.com - Share and work on documents,

Solodox.com - Create, access, edit, share, and collaborate on documents & projects.

TeamWorkLive.com - Track tasks, centralize communication, share documents and files

TheOpenDoc.com - Create multiple workspaces with multiple documents

Thinkature.com - Collaborative workspace with voice chat

Tracbac.com - Workspace, IM, VoIP

Uhroo.com - working on goals, estimates, client feedback

Vyew.com - work on a project and then publish it directly to where you choose on the web.

WebOffice.com - Work on documents

Comapping.com - Mind mapping for everyone from students working together to project management.

Wrike.com - Project management

Writewith.com - Create documents

Yugma.com - collaboration site

Zimbra.com - Email service with collaboration tools.

Zoho.com - Create documents

Kalabo.net - Site for musicians to collaborate on compositions together.

Freepository.com -storage of code to be worked on from anywhere.

Glypho.com - Site for group writing

Novlet.com - Collaborative writing of non-linear stories

WebBrush - graphical sharing and includes drawing tools.

Writeboard.com - collaborative writing, journalists, bloggers and more.

WriteMaps.com - creating and sharing sitemaps

Jamglue - remix your music online

Splice - upload samples, remix

YourSpins - mix your own version of your favorite track, share it and post it

Singshot - the “YouTube of Karaoke”:

kSolo - sing along to backing tracks, and rate the recordings of others.