We have developed PaxMVC, 'javascript thin client + PHP server' framework, to create highly interactive, webtop-like database applications. It allows to create a single-page or pseudo-windowed  Ajax application without any line of Javascript (since all logic is handled by the server).

To overcome some downsides of PHP, Comet technology can be used to communicate with the server. It allows to create really robust and responsive applications.

It's currently under development, but solutions based on our Ajax framework are already used by our customers.