Curious as to why this is allowed

[RidgetOS]

Not going to say much but here:

https://hub.spigotmc.org/stash/projects/SPIGOT/repos/bukkit/browse/LICENCE.txt

Line 34-38

 

[Ally]

Yeah out of context it looks bad, but this is the Spigot repo; and the GNU licence is applied to that alone *. I'm pretty sure that licence doesn't apply to plugins using Spigot since they don't physically share any codebase. You'll have to check Spigot's terms for that. It's actually quite smart, the way Spigot do things since when you create a plugin, you rely on a reference to Spigot itself, not integrating the source into your own plugin.

* and other forks of Bukkit **, which must use the GNU licence.
** This licence is for Bukkit. Of which Spigot is built atop.

Edit, partially wrong. See my next post. LGPL on CraftBukkit.

 

[RidgetOS]

Yeah out of context it looks bad, but this is the Spigot repo; and the GNU licence is applied to that alone *. I'm pretty sure that licence doesn't apply to plugins using Spigot since they don't physically share any codebase. You'll have to check Spigot's terms for that. It's actually quite smart, the way Spigot do things since when you create a plugin, you rely on a reference to Spigot itself, not integrating the source into your own plugin.

* and other forks of Bukkit **, which must use the GNU licence.
** This licence is for Bukkit. Of which Spigot is built atop.

what about the forks of spigot ?

 

[Ally]

what about the forks of spigot ?

https://www.spigotmc.org/threads/whats-spigots-license.415075/

Essentially, tough question. Bukkit uses GPL but CraftBukkit uses LGPL, the difference of which is (for LGPL):

The main difference between the GPL and the LGPL is that the latter allows the work to be linked with (in the case of a library, "used by") a non-(L)GPLed program, regardless of whether it is free software or proprietary software.[2] The non-(L)GPLed program can then be distributed under any terms if it is not a derivative work. If it is a derivative work, then the program's terms must allow for "modification for the customer's own use and reverse engineering for debugging such modifications." Whether a work that uses an LGPL program is a derivative work or not is a legal issue. A standalone executable that dynamically links to a library through a .so, .dll, or similar medium is generally accepted as not being a derivative work as defined by the LGPL. It would fall under the definition of a "work that uses the Library". Paragraph 5 of the LGPL version 2.1 states:

A program that contains no derivative of any portion of the Library, but is designed to work with the Library by being compiled or linked with it, is called a "work that uses the Library". Such a work, in isolation, is not a derivative work of the Library, and therefore falls outside the scope of this License.

https://en.wikipedia.org/wiki/GNU_Lesser_General_Public_License

This should answer your question. Essentially since Spigot is built on CraftBukkit, LGPL applies but doesn't change the effect on forks since it still directly incorporates code base, rather than being linked to it. i.e. same rules apply as detailed above for forks.