We work with use a number of commercial software systems which we like and recommend.
Bynari - Bynari supply a plugin to Outlook (Bynari Connector) which allows the storage of Outlook Calendar items, Tasks, Contacts, etc on an IMAP server. This provides centralised storage, and using shared folders, Exchange like sharing functionality via our IMAP server.
ChatterEmail - ChatterEmail is a powerful IMAP email client for Palm OS Treo based phones. With it you can continuously an efficiently monitor your mailbox from your phone. Because if supports the IDLE IMAP extension, you even get instant notifications when new email arrives.
FastCheck - FastCheck is a small Windows program that runs and sits in your notification tray. It'll let you know immediately when new emails arrive, and allow you to see the email headers and even jump straight to the web interface. It has many configuration options making it flexible for most usage scenarios.
Breevy - Breevy is a text expander and AutoText program for Windows that helps you type faster and more accurately by allowing you to abbreviate long words and phrases -- saving you time and money. Simply define an abbreviation for a longer piece of text, like eml for JohnDoe@email.com. Then, in the future, instead of typing that longer piece of text, type the abbreviation you associated with that text in any application, and Breevy will automatically replace it for you, instantly. Think of how much time you'll save! FastMail users automatically get a 15% discount if you use the link above.
FaxBetter.com - is an internet service that allows you to send and receive faxes over the internet without a fax machine. When you sign up for a free FaxBetter.com account you receive a free TOLL FREE fax number.