I honestly wonder how they do it.

I'm a freelancer and if i work for free, i do not have any money. So for me to be able to develop and share this freely, i would probably need some big corporation that is willing to pay me for working on it.

I'd also be interested in how those projects come up with the money to pay a professional designer. Roundcube looks very sleek, as if it was designed professionally.

BTW, what i'm developing isn't exactly a webmail client. It is an server-side IMAP gateway and a client so that you can use it completely offline.