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 derivatives.
• Artistic (used by Perl), MPL (Mozilla public licence), MIT Licence (used by XFree86), etc.

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