Remember the Milk is a to do list web service. There are some other online to do lists out there, but they fail in comparison to Remember the Milk. RTM is making a great attempt to take on the internet. Any good daily, task/communication oriented web service should have ties into many other web services. Like Twitter, RTM has many different means of connecting and communicating with it over the web.

Admittedly, Remember the Milk's website is not very user friendly. But that's ok, because there are many other ways to access remember the milk. My most favorite is the new gmail gadget that they recently introduced. You can look at detailed instructions for setting up the RTM Gadget here: http://www.rememberthemilk.com/services/gmail/gadget/.

Additionally, for offline addition of tasks, you can take RTM with you in a browser using Google gears.

I can say from experience that there currently exists no other free service for managing tasks as Remember the Milk. I use it mainly for tracking homework assignments.