The first I remember using it was SourceForge (1999).

> To Github, or other "forges."

Then why do they bring Git into the picture? They are not comparing themselves to Git...

> Radicle is a peer-to-peer code collaboration platform (“forge”) built on Git.

This is a word salad that means nothing... more than 99% of moderns software is built on Git in one way or another. Anything that is designed to be used by more than a single user could be arguably called a "collaboration platform". This description completely fails to describe anything useful about the program they are trying to describe. For instance, Git is a peer-to-peer code collaboration platform built on Git. And the same can be said about a huge number of programs that share very little in terms of purpose or application.

When someone writes a definition, s.a. you'd find in encyclopedia, the rule is that it has to (a) link to the broader category of things (b) specify in what way the subject is (mostly) unique in the category (a). If you give only (a), then the reader walks away wondering how is subject different from anything else in (a). If you only give (b), then the reader needs to guess (a), and if they fail, they may misattribute or simply abandon efforts to understand the subject.

This attempt at "definition" is the textbook example of forgetting the (b). It's something that a 10-12 y.o. could come up with... this is not what an adult should strive for.

> They are not. Github is a centralized collaboration platform built on git, and radicle is a peer-to-peer collaboration platform built on git.

You didn't understand the question.