I use Google for my back end stuff and then Thunderbird for Email, with the Lightning Add-on for calendar.
With the right plugins you can sync your email, calendar and contacts for sure.. not sure about tasks and notes.
I have Google for my backend and all my desktops and my ancient Treo 650 all sync up with that... it's a beautiful thing.
If you want to go the Thunderbird route (oh, it's all free too) you'll need:
Thunderbird
Lightning Add-on (Calendar add-on for Thunderbird)
'Provider for Google Calendar' Add-on (Allows read/write sync with Google Calendar)
Zindus Add-on (for the Contact sync)
HTH