So, let me get this straight…
- I cannot share source code or the re-compiled engine
- I cannot share improvements on the engine
- I cannot let players use the engine to create game maps/characters/etc.
…am I right ?
I believe you can IF and only IF they have a subscription to the engine as well.
*What kinds of products can I release under the Unreal Engine 4 subscription plan?
You can release any product that is allowed by law, with the exception of gambling applications and certain safety-critical control systems described in the EULA.
You can release games, demos, simulations, architectural showcases, etc.
The only parts of the Unreal Engine you can’t release to the general public are the source code and tools or modifications to them; these components may only be distributed to other licensees with access to the same version of the Unreal Engine.*
*What modifications can I make to the source code?
You can extend it, modify it, fork it, or integrate it with other software or libraries, with one exception: You can’t combine the Unreal Engine code with code covered by a “Copyleft” license agreement which would directly or indirectly require the Unreal Engine to be governed by terms other than the EULA. For example:
Software licensed under the GNU General Public License (GPL), Lesser GPL (LGPL) (unless you are merely dynamically linking a shared library), or Creative Commons Attribution-ShareAlike License is Copyleft Code.
Software licensed under the BSD License, MIT License, Microsoft Public License, or Apache License is not Copyleft Code.*
Can I share the Unreal Engine source code or tools with others?
You can share the source code or tools, along with any modifications you’ve made, with anyone who is an Unreal Engine licensee who is authorized to access the same version of the engine as yours, e.g. the 4.x.x version number of your installed build.
-From Frequently Asked Questions - Unreal Engine on 20 May 2014