Is there a page on this wiki or another that gives an overview all software projects that are possible related to Wikimedia? For example, the organization of WMF developer teams, toolforge, wikimedia cloud, external desktop and apps/websites, and userscripts.
If not, should I create one?
No (as I don't see which problem a single page would solve), and no (as someone would have to have a complete overview plus maintain that page for years to come). :)
The page will not be a complete list of all software in Wikimedia, but a general overview on the large stuff and how it is connected. For example, how all of the Wikimedia product teams work and what they work on, what Wikitech is, how Toolforge works and what it's used for, what is WMcloud WMFlabs, what are/is the difference between userscripts and modules, and how people connect to MediaWiki using APIs.
> I don't see which problem a single page would solve
Right now new developers have no way of understanding the "development strucuture" of the Wikimedia community or a list of broad software projects they can work on and see who works on it. I personally am a relatively new developer and it took me about a period of 3 months to eventually learn what all of those things mentioned above are, what they do, and what their differences are. Such a page would allow developers to see how "Wikimedia works" and where they should look say they want to develop a tool for a wiki, an application using data from a wiki, or contribute to the development of MediaWiki itself.
I think the up-coming Developer Portal might be working towards something like what you're describing.