Rainmeter is open source, and while few, there are restrictions on what you can do with the source code for Rainmeter. Mostly you agree not to try to make Rainmeter NOT open source. If you want to take the code, change and add to it or improve it in some way, call it HaroldMeter, and give it away or even sell it, that's entirely fine, as long as HaroldMeter is also open source, you credit Rainmeter for the original code, provide access to your source code, and allow further derivatives of it to be freely made.
However, the skins you create with Rainmeter belong to YOU, and you can do anything you want with them.
If you are planning to create skins for profit though, be aware that we won't allow or support them on these forums, as that is not what
this Community is about. Any discussion about a skin that is in any way being "sold" is in effect "advertising", and we do not allow advertising for any commercial products on these forums.
The terms of use for the Rainmeter application and source code is a link to the
GPU GPL/v2 license in About / Version.
Basically that says:
1) You may use the program as you like.
2) You may modify the code any way you want, and even redistribute it as your own.
3) You may use any part of the code in your own programs.
4) You certainly may sell any program you create using the code.
5) You must give credit to the Rainmeter project if you use the code.
6) You must make any program you create with the code also open source, and provide access to your source code.
Open source means "free" in the sense of "freedom", not in the sense of "price".
You may use, modify, derive from, bundle, and even sell Rainmeter as you see fit. What you can't do is break the chain of "open source", take ownership of Rainmeter or derivatives of Rainmeter, and lock it down in a proprietary way. Open begets open, that is the entire and only point.
There are no terms of use defined by us for skins created with the tool, as those are your intellectual property, and you can do whatever you like with them. Many folks license their skins with a
Creative Commons Attribution-Non-Commercial-Share Alike 3.0 license, which has the right tone as far as I'm concerned, but that is entirely up to you.
Basically that says:
1) Use my skins as you like.
2) Modify my skins any way you want, and even redistribute as your own.
3) Use any part of my skin code in your own creations.
4) Give me credit if you use my skin code. (Attribution)
5) Don't "sell" what you create using my skin code.(Non-Commercial)
6) Apply this same license to the things you create using my skin code. (Share Alike)
To be honest, given that every skin ever written is based in some way on what others have done in the past, what authors have learned from the efforts of others in the community, any license on a skin is pretty much unenforceable anyway. It's just locks to keep honest people honest.