A web based groupware / collaboration suite with all of the standard features (email, calendar, contact management, chat, message board and file repository). Groups provides one of the most robust web based groupware experiences in the industry while still being highly customizable and easy to integrate with existing systems and data stores.
Oddpost and Gmail have nothing on this web-based email client!
Email
All the "normal" email features (create, reply, forward, delete etc)
Drag and drop email management
Rich text email so you can make it pretty if you really, really must
Greatly reduced virus risk as message content is not automatically run without your consent
Out of office reply
Configurable layout, fonts and default window sizes
Completely customizable
Completely cross-platform
Completely web-based so can be accessed from anywhere
Easy email search
Share in-boxes without having to share read/unread statuses
Calendar
View by day, week and month
Hourly overview
Assign events to a particular category (categories can be limited to a single user, shared among a defined set of users or completely public)
Search for events
Invite others to a particular event
Set up repeating events
Bulletin Board
Threaded conversations
Edit your previous comments
Sort into categories
Chat
View other chat participants
Quick and easy web chat, no download required
Archive chat transcripts
Multiple chat rooms
Contact
Assign contacts to one or more category (categories can be limited to a single user, shared among a defined set of users or completely public)
Create company records
Capture all the usual personal information used by personal digital assistants
Keep track of communications with that client
Document Management
Assign to a category (categories can be limited to a single user, shared among a defined set of users or completely public)
Lock files if they are being updated to prevent users from overwriting them
View document change history
Keep track of which users have read or still need to read a given document