Mozilla Thunderbird gets a web-based open-source client to take on Gmail
There's a slight catch, though.

We didn't realise it at the time, but 2004 was the beginning of something huge for email. During the year, we saw two seeds planted in the digital mail sphere: Gmail on April 1st (yes, and we thought it was an April Fools joke because of it) and Mozilla Thunderbird in December. Only one of them would become a household name, while the other would slip into mild obscurity.