These icons are made as a replacement for the placeholder icons used by the new Qt graphics toolkit that ships with the upcoming Octave 4.0.
At the moment Octave uses the Tango icon set that misses a lot of icons that are usefull for Octave. Since I found a lot of joy in creating the icons thus far and also highly dislike the general appearence of Tango I'm going to add a lot more icons in the future (not restriced to the plotting figure). Maybe I'll get a complete icon set together.
All icons are released under the GPLv3, check the license file inside this repository for more information.