You can find the repository here: https://github.com/enigma-dev/Calico-Icon
This project is meant to create a simple, free alternative to icon sets such as Silk, which have licenses just annoying enough to be GPL-incompatible. While I respect icon authors' wishes to be credited for their work, I also respect free software programmers who want to release their applications without worring about license violations.
All the icons in this set are vectorized, but designed to look good at small resolutions. You can, of course, render them at larger resolutions, but due to SVG's lack of hinting, this might turn out bad at magnifications under 2x, and due to their design focus on small resolutions, they might not look that great at larger sizes, anyway, from the 1px lines accounting for 5% of the icons' screen space.
Presently, this icon set is small. It is designed to suit the needs of various IDEs for the ENIGMA project, and so will accumulate more icons as the need arises for them in that project. You may request new icons in the tracker.
The icons are designed to be minimal, in the sense that it is easy to change them in bulk in their vector format. SVG is not a perfect format, but it is much better suited for this than, say, XCF or PSD.
That said, enjoy the icons.
These icons are licensed under GNU GPL v3, you can find the full disclosure on their website. You are free to copy, share, and modify these icons under the terms and conditions of the agreement.
These icons are comprised of various board smileys in SVG vector format, right click to enlarge them or download them as png, left to get the SVG version.