Thunderbird is a free and open-source email client developed by the Mozilla Project. It is available for Windows, MacOS, and Linux in many various languages. The newest version of Thunderbird can be downloaded on
www.mozilla.com.
Thunderbird supports both POP3 and IMAP (and other formats, e.g. RSS feeds)
If you do not know the difference between POP3 and IMAP some additional information can be
found here. If you are still unsure, try POP3 first.