How to compile CoffeeScript on save in VIM (arnklint.com)

I guess a SASS version could also work?

Yes, it should be as easy as autocmd BufWritePost,FileWritePost *.coffee :silent !sass --update <afile>

coffee-mode.el provides the same functionality for emacs. Automatic compilation of any *.coffee file on save can be enabled by

    (add-hook 'after-save-hook
                          (lambda ()
                            (when (string-match "\.coffee$" (buffer-name))
                              (coffee-compile-file))))

coffee -w

The CoffeeScript compiler is very fast (takes <100ms for a typical file), so this is a fairly good approach for most development.

However, it's worth noting that there are other projects that let you stop thinking about compilation altogether. If you're developing for Rails or Python, for instance, you can just use a plugin. (And as of Rails 3.1, you don't even need one.) If you're just developing a static site, I like The Middleman (http://middlemanapp.com/), which does on-demand Haml, Sass/Less, and CoffeeScript compilation, then lets you bundle it all up (minified) for deployment with a single command.