Taken from a Wikipedia search for forge + software :

In FOSS development communities, a forge is a web-based collaborative software platform for both developing and sharing computer applications. The term forge refers to a common prefix or suffix adopted by various platforms created after the example of SourceForge. This usage of the word stems from the metalworking forge, used for shaping metal parts.

For software developers it is an online service to host the tools they need to communicate with their coworkers. The source code itself is stored in a revision control system and linked to a wide range of services such as a bug database, continuous integration, etc. When a FOSS development community forks, it duplicates the content of the forge and is then able to modify it without asking permission. A community may rely on services scattered on multiple forges: they are not necessarily hosted under the same domain. For instance it is not uncommon for discussions to be hosted on Discourse while the source code is hosted on Gitea.

For users, a forge is a repository of computer applications, a place where bugs can be reported, a channel to be informed of security issues, etc.

Software forges became popular in 2001,[1] and have proven successful as a software development environment for millions of software projects.