copyleft-next
An experimental copyleft licence that tries to do what the GPL does in a fraction of the text.
Richard Fontana, then a lawyer at Red Hat, started the project in 2012 as an explicit rework of GPLv3. That licence runs to more than 5,000 words, full of terms only lawyers and the Free Software Foundation fully understand. copyleft-next strips most of it out, keeps the requirement that derivative works be distributed on the same terms, and is explicitly GPL-compatible. Development happens in the open in a public repository where anyone can propose changes — itself a pointed contrast with the FSF's more closed process.
Adoption has been thin. The best-known users are a few test modules in the Linux kernel, dual-licensed under GPL-2.0 or copyleft-next, which have generated more mailing-list discussion than the code itself.