Gmail is an email client. Facebook is now, too. So are the default 'mail' applications for Android and iOS. And let's not leave out Emacs :)
The challenge of email (which comes with its advantage of being ubiquitous today) is its plethora of standards documents one must read and respect if one wants to make a serious go of developing software that will work well with most of its corner cases.
I'd hazard a guess that none of the examples you gave were easy to code :-) Also, I'd argue that Gmail and Facebook type clients are non starters as its hard to do meaningful encryption in Javascript since you always must trust the server.
But if you disagree, please write one - I'd be a very willing beta tester and would even be keen to help in a limited way.
I'm not saying it'd be easy to just sit down and code one weekend! But really, are we expecting the "federated social web" people are talking about to be much easier to code than email software? We want it to do much more stuff, so it'll probably be harder.
Also, I think it's implicit that you trust your server. It's other people's servers you've got to worry about.
I just thought of another potential challenge - SMTP limits. I think Gmail limits you to sending 40 messages per day for instance. This sucks if you have >100 friends.
Those limits are imposed by existing email software. The real underlying challenge you are getting at is dealing with spam. And that would be just as much a challenge with any distributed social network too, for more or less the same reasons.
Email did this badly from the start, because it started in a much more trusting world of people who did not spam one another. Authentication features were added later, but there was no requirement to use them, which limits their effectiveness.
Perhaps for a project starting fresh now, this can be handled better?
http://catb.org/jargon/html/Z/Zawinskis-Law.html
Gmail is an email client. Facebook is now, too. So are the default 'mail' applications for Android and iOS. And let's not leave out Emacs :)
The challenge of email (which comes with its advantage of being ubiquitous today) is its plethora of standards documents one must read and respect if one wants to make a serious go of developing software that will work well with most of its corner cases.