Outlook Google Calendar Sync - Offers calendar synchronisation between Outlook and Google, including attendees and reminders.
imapsync - Console-based utility for migrating IMAP mailboxes.
GO Contact Sync Mod - GO Contact Sync Mod is an open source tool to synchronize your Microsoft Outlook contacts with...
MailStore - MailStore Home - A 100% free single-private-user desktop solution
gSyncit - gSyncit Outlook Cloud Synchronizer. Outlook Calendar, Contact, Task, Note Synchronizer supporting Google, Toodledo, Evernote, Informant, iCloud, AOL, Yahoo, Synology, Fruux, Memotoo and CalDav/CardDav services.
Fetchmail - The Fetchmail Project