I've been looking at Wt (pronounced Witty), via Heartless on #php, for the last 30 minutes or so. I've got to say, I'm pretty impressed.
The name and concept seems inspired from Qt, or perhaps WxWidgets, and is quite robust. Hardly pretty at this stage and I've not yet hacked anything together, but quite cool. Especially if you insist on using C++ to develop your websites.
Edit:
Paul / Chip has a very good point on using Wt;
On Wit -- It takes the approach of a Widget Toolkit, heavily mixing the presentation with the 'business logic', in my experience these type of toolkit designs end up not working so well. I prefer the separate template file, which contains all of your design -- the code just sets some variables for it, ala ClearSilver or somewhat how Smarty works in PHP.
Given my frustrations in the past, in dealing with ultimatums from designers (despite implementing templated systems), I can fully understand Chip's point... Things never look as good as they initially do. Arses.
On the plus side, Chip appears to be throwing his hand into a web toolkit of his own. It'll be interesting to see what he throws together.
It depends on how you code, as always. Just because you can put the business logic into a C++ application, you do not have to. Just have the C++ application call the business logic on a separate daemon, for instance a Java server running ZeroCs I.C.E. or a CORBA implementation. Meanwhile, Witty has gotten itself Ruby port. Check it out! http://wiki.github.com/rdale/wtruby/tutorial