Yahoo's open source framework combines YUI on the client, Node.js on the server, and excellent use of MVC design patternFollow @peterwayner
Node can be incredibly fast, but it achieves much of this speed by operating without a safety net. If your code locks up, the entire server locks up with it. The most cultish devotees feel that this can be dodged with careful coding. Mojito encourages this care by offering the well-understood paradigm of Model-View-Controller, or MVC. Splitting the code into small distinct parts that serve predetermined roles makes it less likely that you'll lock up the server. That's the theory, but of course nothing can stop a determined programmer.
Mojito's MVC structure emulates the ideas and design paradigms that emerged from other Web programming worlds. The Java server-side programmers are so devoted to frameworks like Struts that you could get yourself stabbed in a Java bar if you even hinted that MVC is not right for all things. The paradigm succeeded because it brought some order and roughly approximated the way that development teams are organized. The people who are good with visual design end up in charge of the View; the people who organize the data (often DBAs) create the Model; and the programmers handle the Controller that makes decisions about what the data can do (the business rules).
Mojits and MVC
The Mojito framework makes excellent use of the MVC paradigm. Each Web application is broken up into mojits -- shorthand for Mojito widgets. Mojits are rectangular areas of the page that are meant to be fairly independent. You should be able to mix and match mojits if you're careful in your coding; you may also want to get them talking with each other.