Apple's new OS X 10.4 Tiger has a new feature called Dashboard. In your Dashboard you can run little widgets which are a combination of HTML, Javascript, CSS, and sometimes specialized plugins. I've found that those which don't require a plugin can be run from the browser.
The widgets live in :Library:Widgets and are really specialized folders. Right click (control-click) a widget and choosing Show Package Contents to look inside. Typically there's a single .html file, which when clicked will open up in Safari.
Some widgets require special plugins and won't run.
Note: if the first two open up and the window is blank, click in the window and refresh (cmd-r or ctrl-click (right-click) and reload).
Just a quick experiment. Other Dashboard items might work, all depends on if they require a special plugin or not. Simple ones and web based ones seem to work best.