Chromium and Google Chrome (version 4 and higher) have built-in support for Greasemonkey-style user scripts.
To use, click on any .user.js file. You should see an install dialog. Press OK to install.
The preferred way to specify the pages that a user script should run against in Chromium is the @match attribute. Here are some examples of its use:
// @match http://*/*
// @match http://*.google.com/*
// @match http://www.google.com/*
See these comments for details on the @match syntax.
Support for Greasemonkey-style @include patterns is also implemented for compatibility, but @match is preferred.
With Greasemonkey-style @include rules, it is not possible for Chrome to know for certain the domains a script will run on (because google.* can also run on google.evil.com). Because of this, Chrome just tells users that these scripts will run on all domains, which is sometimes scarier than necessary. With @match, Chrome will tell users the correct set of domains a user script will run on.
In Chromium/Google Chrome, Greasemonkey scripts are injected by default at a new point called "document-idle". This is different than Greasemonkey, which always injects at document-end.
The document-idle injection point is selected automatically by the browser for the best user-perceived performance. If the document has many external resources like images that slow down page load, the browser will run the script at document-end, like Greasemonkey, while waiting for resources. However, if the page loads quickly, scripts may not be run until after window.onload has occurred -- much later than with Greasemonkey.
The main impact this has on script developers is that you should *not* wait for window.onload in Greasemonkey scripts intended for use with Chromium/Google Chrome, because it may have already occurred when your script has run.
Note that there is normally no reason to wait for window.onload in any Greasemonkey script, even in Firefox. Document-end and document-idle are both guaranteed to run after the entire DOM is parsed, which is the usual thing script developers are interested in having occurred. If for some reason you really need your script to run after window.onload, you can check the document.readystate property. If it is "complete", then you can assume onload has occurred. If it isn't, then you can listen for onload.