GNU GPL
The GNU GPL is the most widely used free software license and has a strong copyleft requirement. When distributing derived works, the source code of the work must be made available under the same license.
GNU AGPLv3 GNU GPLv2 GNU GPLv3
Required Permitted Forbidden
Disclose Source
License and copyright notice
Same License
State Changes
Commercial Use
Distribution
Modification
Patent Use
Private Use
Hold Liable