Frictionless can be used as a to-do manager, just like many other GTD programs. Frictionless is unique because the developer designed it around linking to other programs that you use in your digital world. Frictionless is open-source and written in Ruby Cocoa. This allows it to be extended by others and can connect to data stored on Google.
The interface is flexible and deep, as it was designed for someone with 100+ items on their to-do list, of which only 10-20 could be completed at any given time. The interface is designed to quickly filter out items you don't need and focus on the items that you can actually be working on.
Version 2.0d18 fixed the problem bringing up NSAlerts that was hitting a few newbies.