I went trough all mods posted to Kerbalstuff and counted them by their license.

There's several issues I'd like to point out.

Proper Licenses

Some mods don't set a proper license (such as "do what you want", "no license actualy", "dwtfyl", etc.) . This makes it difficult to know what people are allowed to do with them. These are particularly numerous in the Public Domain, Other and All Rights Reserved categories.

• If you want to dedicate your work to the public domain, proper license identifiers to indicate this are CC0 or Public Domain.
• If you want to retain all rights in your work, the proper identifier is All Rights Reserved
• I would strongly discourage you from using your own license text and pick a popular license such as CC0, MIT, BSD, etc.

Typos and varying license identifiers

A number of mods spell out the license identifiers in incorrect ways. It'd be good if Kerbalstuff had a dropdown with defaults for popular licenses.

Non distributable mods

If you choose "All Rights Reserved" (or equivalents) you make it impossible for others to share your mod.

Non derivative licenses

If you choose "All Rights Reserved", CC-BY-ND, CC-BY-NC-ND then others cannot remix, adapt and update your mod. 40% of Mods that choose a non derivative license are updated to KSP 1.0.5. 52% of Mods that choose another form of license are updated to KSP 1.0.5.

Restrictive Incompatible licenses

Not all licenses are compatible to each other. Creative commons defines a license compatibility matrix for their licenses.

The three mutually incompatible popular licenses (apart from non derivative licenses) are:

• CC-BY-NC-SA,
• CC-BY-SA
• GPL

This means that authors who choose such a license, cannot benefit from what authors using a different one of the restrictive licenses did and vice versa. It also means that a mod that wishes to combine content from other mods with a different one of these licenses cannot do so.

These licenses are also infectious, and force a mod-author to adopt this license if they wish to build upon your work, hence furthering the proliferation of mutual incompatibility.

I'd recommend:

1. It is likely you do not require a restrictive license, please consider using CC0, Public Domain, MIT or BSD
2. If you do require a restrictive license, please consider cross-licensing your mod in all three of these licenses

Non commercial

Some licenses in use for mods are of the Creative Commons non commercial variety (CC-B-NC-SA, CC-BY-NC-ND and CC-BY-NC).

The creative commons non commercial clauses are somewhat controversial, and can lead to unintended chilling effects. It's beyond this summary to discuss this topic, but if you can, please choose a license that does not use a non-commercial clause.