Fernando,

There is a widget for the dashboard (http://www.apple.com/downloads/dashboard/business/rememberthemilkwidget.html ) and an application for the mac which is currently in process (I am using it with few issues) http://www.chrillo.info/app-for-the-milk/

Hope this helps
Leah

Another approach is to use Fluid. Fluid is a "site specific browser" (SSB). In essence, what Fluid does is restrict itself to one site. So, I created a SSB for RTM, and when I launch it, I only get to RTM. That way it doesn't compete with all the browser windows I have open.

You can also try Google Gears if offline functionality is what your looking for (http://gears.google.com/). I've experienced a couple bugs here and there but if you know what your doing you'll be fine.