Network copyleft
The licence family that treats letting people use a program over a network as distribution, and so demands source code even from those who never ship a binary.
Ordinary copyleft triggers on distribution, and a web service distributes nothing. The Affero GPL of 2002 was the first attempt to close that gap; AGPLv3 in 2007 is the one that stuck. Lawrence Rosen's Open Software License 3.0 does the same through the notion of "external deployment", and the EU's EUPL 1.2 explicitly counts providing online access to a program's essential functions. The Cryptographic Autonomy License, OSI-approved in 2020, goes furthest and covers users' data too.
MongoDB's SSPL of 2018 pushed the logic until it demanded source for the entire service stack around the program, which the OSI declined to approve. What the whole family shares is that many companies, Google most famously, ban it internally — which, for some authors, is precisely the point.