There are many oldish licenses that allow modifying code but require sending all modifications to the original developer of the software. I believe that's what

There are many oldish licenses that allow modifying code but require sending all modifications to the original developer of the software. I believe that's what's being referred to. Some of them are listed in the GNU license list [1]: AT&T Public License, Reciprocal Public License, Open Public License, eCos, Plan 9, APSL v1, and (not old, and hence obnoxious) the Oculus Rift SDK license. [1] https://www.gnu.org/licenses/license-list.en.html https://www.gnu.org/licenses/license-list.en.html