Clearbit - Clearbit provides Business Intelligence APIs
imapsync - Console-based utility for migrating IMAP mailboxes.
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.
MailStore - MailStore Home - A 100% free single-private-user desktop solution
InsideView - InsideView aggregates and curates all the company and contact data, news and social insights, and professional connections you need to do business better.
Fetchmail - The Fetchmail Project