Boolean: GDSII viewer/editor + (boolean) operations on sets of 2d polygons.
Boolean Web Site:
http://boolean.klaasholwerda.nl/bool.html

Copyright section form the site:
The code is written by Klaas Holwerda,  it is free to use for non commercial open source projects licensed as GPL.

Note:
License info in kbool files:
files are under wxWidget license