Follow up: license_change
Compared to GPL, LGPL allows people to use the program under LGPL (let's call it the “free program” or “free code”) with their non-GPL code, IF they do both of these things:
In practice, currently this means that people can make a Minetest mod and write “Do not distribute” to it. People who want to create something based on Minetest as their day job will want to do this. We can discourage it, but the benefits would be minimal, whereas we might stand to gain users by licensing more permissively.
If Minetest (or code taken from it) gains any binary interfaces, people can write proprietary programs to interface with it as a DLL.
You can always relicense a LGPL program under GPL. We should give LGPL a chance, and if it ends up not working as well as we hope, we can just continue under plain GPL. You cannot do it the other way without agreement of all contributors, which is getting harder and harder as time goes.
GPL software can be sold Yes it can be, but as users are not legally obliged to buy the code, you cannot risk to build business on it. Minetest thrives on creative code; not creative textures. Some games have large pre-made worlds as the main selling point. Minetest does not.
We will lose our users to the proprietary world The proprietary people are on completely different markets than we currently are. The only thing they can do to us is bring more people in, as people see their creation and get interested of the technology behind it.
We will lose contributions No we won't. Nobody from the commercial business has contributed anything to Minetest yet. Using LGPL that is way likelier (as it wasn't really even possible before).
Also, the current Minetest developer/user base is very OSS minded and they're not likely to just go nuts and try to sell every small bit of their work as proprietary. Libre code will always be encouraged and respected.
We will lose <anything else> No we won't.
We don't need any more freedom than GPL gives While that may be true, again, this move is targeted at commercial programmers. If they're going to use the software to build something, they need to be able to do it in secrecy, at least according to modern software development models. Maybe while they're around, we can convince them otherwise, but the biggest concern is getting people interested in using the engine.
Proprietary software is cancer The Minetest developers largely agree, and want to help build a cool, free game, but there are also a lot of other concerns about how to bring people into the project, and this is one option currently being explored.
I, celeron55, have decided to attempt to relicence the code as LGPL. In the future, this will make the code more worthy for separating into a library (or a few), and will also free up the atmosphere in terms of how people new to the project view using it as an opportunity to make different games (as it is becoming more and more like an engine).