free hand drawing, basic shapes, upload images

No registration required

Browser based, no plugins required. Very simple interface.

chat box

sharing is done manually, by sending people the URL

drawing exportable as image

functions to clear drawing, background, all

Sticky note board

Stickies can have text, images, photos from webcam

Flash-based

No registration needed

Anonymous access can be password protected

Sharing by email, sending URL

Exportable to PDF, Excel and CSV (but includes only the text)

No function to clear the board

Free (with restrictions)

browser-based (HTML5)

No registration required, but possible

Participants don't need registration. Invitation by e-mail

Boards can be zoomed in/out

Colourful stickies, icons, arrows and boxes

not very fast

Exportable to PDF and PNG (as image)

History view of changes, with replay

No way to erase the board

No registration required or even available

To share, manually send the URL by e-mail

open source (Github)

It can be installed locally (Node.js)

Index cards on whiteboard metaphor

very simple interface. All changes are real time for everyone.

No export function

Collaborate on documents like spreadsheets, text documents, presentations, etc.

Google account required for all participants

Sharing done by e-mail notification. Owner must send invites from site

Chat function

No registration required (nor available.)

Browser based

Text sharing

Time slider feature to see evolution of changes

Save revision (snapshots) with restore

Export to HTML, TXT (PDF not working)

Chat window

Authorship colours (to identify who wrote what)

No way to delete the documents

free w/registration

Collective decision making

free account (limited to 1 "group")

Scheduling polls

Registration required to create boards. No anonymous access

Mind-map style diagrams, with connected nodes

Sharing is done from the site, one user at a time, and seems buggy when inviting someone that isn't registered yet

Users can't change their name

Exportable to PDF and image

Flash based

Free. Real-time update only in paid version

Fixed columns: To Do/In Progress/Verify/Done