How can you manage your project?

Question

Project management

Hey!
Let's say I have a certain service, let it be a social network site.
As the site grows, its functionality and design grows, and there are many different nuances that need to be taken into account.
Is there some kind of software in which all this is described: design, functionality, features, access rights, programming languages, who is allowed to which module of the site, etc.?
Here, for example, VKontakte, how did you develop the service? Do they keep some kind of internal documentation? After all, this site is very large and if you do not keep some kind of record of its condition, then you can just get confused.

Answer 1

Wiki?

Answer 2

If there is no money at all, then Redmine.

Answer 3

Google Docs?