In my understanding, GPL is a copyleft license where your code can only be used in open-source projects (vs permissive licenses where your code can be used in closed-source projects).
Based on a few quick searches and my general understanding, it seems that AGPL is a more restrictive license where closed-source projects can’t depend on your code at all (?) and LGPL is a more permissive license where your code can be used in closed-source projects (?).
edit: After a bit more searching, I found that LGPL is still a copyleft license but a “weak” one. It looks like LGPL code used in other projects, if in their original form, can be closed-source but must be open-source if there are any changes. What constitutes as a change? Do ports count? How about updating syntax, like Python 2 to 3?
Also, it seems that AGPL might be almost the same as GPL (both are “strong” copyleft licenses) where AGPL just has a clause for source code sharing when it is shared over a network. In that case, why use GPL over AGPL, and vice versa? There seems to be many projects using GPL, so what is the downside to AGPL? Is the network sharing thing a bad restriction for some people, and why?
(back to original post from here)
I could be wrong on some or, more likely, all of those points. I also have a few questions. What is the difference between GPLv2 and GPLv3? If LGPL is more permissive, what are its differences compared to a license like MIT? Why would you go for one or another? And for AGPL, why would you prefer one over another? Is it simply how much (or really, how little) you want your code to be used in closed-sourced projects? And how do all these licenses interact with each other? Can you use GPL code in AGPL projects, and vice versa? What about LGPL code, is that too permissive for GPL or AGPL or can it be used in those projects?
For your first paragraph: yes, exactly. For software you distribute in binary form to customers, GPL and AGPL are effectively the same thing. For SaaS you can easily use GPL and not share your source code. Though beware if your ever need to deploy your SaaS on the customer's premises.
The point of these licenses is to not restrict user's rights, so LGPL doesn't want you to use their code and not let the user do whatever they want with it according to LGPL. So if I create an app and decide to not maintain it, you're still able to pull bug fixes etc. even without my involvement.
Yes, GPL effectively makes your binary GPL as well. And if you provide a library for others using GPL code, projects using your library must be GPL-compatible as well.
But the point is that you cannot restrict the user's rights, so if you distribute the source code you can choose a more permissive license (like MIT) for your code. That could in theory mean that if someone finds a replacement for your GPL dependency and remove it, they could release it under any MIT-compatible license (which is just about anything).
GPL dependencies are often avoided in companies because of its spreading nature where it makes everything it touches effectively GPL. And even if you write SaaS, if you're B2B you'll eventually land a bigger customer with strict software policies and you'll have to deploy on customer's servers, thus having to legally distribute the source code as well.
Ah okay, that makes sense. So “replacing” parts of a project would mean switching dependencies from something that’s GPL to something else (e.g. one that is MIT licensed).
Yep.