The following are all free programs that can be used to replace outlook.

Thunderbird

This is the most popular free email client solution on the net and is updated on a regular basis. To set Thunderbird up with a calendar can take a bit of time and will require some IT skills. I am sure over time it will get improved and the installing of the calendar will get easier.

• completely free for home and business
• lots of settings and can be tricky to set up
• no inbuilt calendar (see below)
• an integrated calendar can be added by using the standalone cross platform calendar program, Sunbird. Sunbird can then be intergrated into thunderbird by using the extension Lightening. This extension does heavy integration so it performs like outlook.
• it is possibly to import outlook addresses and emails into thunderbird via the inbuilt wizard. Disable antivirus and firewall as this could cause issues (M$ av did, it causes the import to hang/get stuck)
• to get calendar items into Sunbird/Lightening you need to export from Outlook in ICS (prefered) or CSV format and then import into Sunbird
• to show the calendar tab, top right there are some icons, the one that looks like a calendar click it to show the calendar
• when setting up an email profile in thunderbird to complete the email account setup without veryfying details, click advanced config
• signature handling is a bit shit - you can only specify 1 signature, the rules on how the signature is attached is shit
• the creation and manipulation of emails is limitid to almost text only, no proper WYSIWYG
• it is possible to export data if you want to move client at a later date

EM Client

This client is free with caveats and there is a pro version, however it looks exaclty like outlook including a calendar and you can completely import all of your outloook in one import wizard which consists of a few clicks. For free this is fantastic and easy to use.

• Free version only allows up to 2 email accounts, this is fine for most.
• when you install the free version you get 30 free trial of the Pro version. After this you need to install a license file for both the Free and Pro versions. To get a Free licsense you need to apply on the website and fill in a questionaire, this questionaire needs to be filled in once a year to renew the license.
• Pro version is not limited
• the 2 licenses are. Free/Home/Personal/Non-Commercial and Company/Commercial
• identical to outlook in useability and feel
• imports all settings ie accounts, signatures, emails, calendar items and more
• import wizard is a few click to perform a full import
• it is possible to export data if you want to move client at a later date

Zimbra Desktop (by VMWare)

This is Ajax based client which acts as a normal client unless you want to use the advanced Zimbra Account with an appropraite server. The local and the cloud repository sync with each other when using a Zimbra account. This would not be an ideal outlook client replacement at the minute beacuse of the time involved migrating to this from outlook, but it could be a very good email client on its own. Importing and exporting could be tricky

• You can use Zimbra Client for normal email accounts (ie not Zimbra accounts) and it only stores your files locally and as such acts as a normal email cleint
• can be cloud based with synced local repository if you use a zimbra account and am appropriate server
• can send in both html and plain text (this is default)
• has calendar
• GUI seems web based
• Open Source Edition (Free) and Paid versions, compare editions here
• searching in the trash and spam folders is off by default
• can handle signature properelyy and supports HTML and plain text signatures
• can add social media feeds (Twitter/Facebook.Digg)
• briefcase feature
• tasks
• email/address book/calendar/tasks/briefcase export feature. Proprietry Format
• import Feature but unkown what it will import, it might only be previous Zimbra backups
• Zimbra Desktop FAQ is here
• works by running its own webserver @ http://127.0.0.1:49832

Other Clients That have been looked at

• Opera Mail - built into opera and is fiddly
• SeaMonkey  - more a pack of cutomised mozilla product, no calendar
• Spicebird - not updated often but could be because it is a new project
• PhoenixMail - old and outdated
• Pegasus Mail - modern client but no calendar
• Microsoft Entourage 2008 - mac only
• Evolution 2.28.2-1 / Evolution Groupware Suite - looks like outlook, only for linux
• Windows Live Mail - basic email client but is reliable, is part of Windows Live Essentials
• Incredimail 2 - advertising and stupid icons etc.. some people might use it at home, free version has adverts on emails,
• FreeMailCommander - free and paid versions. free version is ok for home people but does not support signatures unless you get the paid version, not bad looking but layout is a bit messy
• Claws Mail - This is an open source client that has an active community and is kept upto date. It is ported to most platforms and has calendar and address book plugins amongst others.

To export outlook 2010 calendar

1. select calendar and then the file menu
2. save calendar as file, make sure you set all items to export, this will export a ics format