Developer website: Twin Forces
Frictionless is a to-do list manager just like the many other GTD programs out there. Te main thing that makes Frictionless unique is that the developer is designing Frictionless around linking it to the many other programs you use in your digital life. To facilitate this, not only is Frictionless open source, but it's written in Ruby Cocoa so that it can be easily extended by others, and so that it can reach out to connect to data stored on the Internet as well.
The user interface is also quite deep and flexible, designed around the person who has 100+ item to-do lists, of which only perhaps 10-20 items could actually be performed at any one time. That is, the interface is designed to let you quickly filter out all the items you don't want to look at in favor of the items you could actually be working on right now.