Popular licences for free software
- GNU GPL (general public licence) - requires that all derived
works are also released under the GPL.
- The BSD Licence - anything goes.
- GNU LGPL (lesser general public licence) is a half-way house.
It allows linking to proprietary code, but not proprietary
- Artistic (used by Perl), MPL (Mozilla public licence), MIT
Licence (used by XFree86), etc.