Ditrit project is a programmable application launcher that tries to "do the right thing" for any input. If ditrit is given an email address, it knows to launch your email client and compose an email to that address. Likewise, ditrit knows to open URLs in your browser, text files in your text editor, and AIM screen names in your IM client.
Ditrit reads its input from stdin or from the X Windows primary selection (aka clipboard). The ditrit configuration file consists of template regexps and commands. The templates are matched against the input. When a match is found, the corresponding command is run. The input can be wholly or partially inserted into the command line.
To read from the X selection, you'll need >>python-xlib in your PYTHONPATH when you run ditrit.
Ditrit's name comes from pronouncing the acronym DTRT, or >>Do The Right Thing.
There are similar CGI scripts on the web (impressive.net, >>aaronsw, >>clemens radl), but they're specific to the web. More importantly, the user must explicitly say what they want to do - define: for dictionary, movie: for movie listings, etc. You don't have to tell Ditrit what you want to do; it uses heuristics to guess on its own, based on the input.