My Favorite Free Alternative Applications

I was playing with Pearltrees, putting together all the major alternative applications I use that are open source. One of the most important criteria is that a version exists for Linux and Windows. Here it is:

Thinking Space - Android App

A friend found this one and it is a good one. I guess it could be used on a phone, but better for a tablet.  Thinking Space is a Mind Mapping application for Android.

Thinking Space - AppBrain link.