The open patent movement seeks to build a portfolio of patented inventions that can freely be distributed under a copyleft-like license. These works could be used as is, or improved, in which case the patent improvement would have to be re-licensed to the institution that holds the original patent, and from which the original work was licensed. This frees all users who have accepted the license from the threat of lawsuits for patent infringement, in exchange for their surrendering the right to build up new patents of their own (in the specific domain for which the original license applies).
The open patent idea is designed to be practiced by consortia of research-oriented companies and increasingly by standards bodies. These also commonly use open trademark methods to ensure some compliance with a suite of compatibility tests, e.g. Java, X/Open both of which forbid use of the mark by the non-compliant.
On October 12, 2001 the Free Software Foundation and Finite State Machine Labs Inc. (FSMLabs) announced a GPL - compliant open-patent license for FSMLabs' software patent, US 5995745 . Titled the Open RTLinux patent license Version 2, it provides for usage of this patent in accordance with the GPL.