A lot of people don't seem to be aware that the Stack Exchange network consists of lots of different sites. StackOverflow is just the biggest one, but there are sites for all sorts of discussion: https://stackexchange.com/sites

Those sites all work exactly the same as StackOverflow and you can login with a single account. Just the rules regarding content are different. See for example https://softwareengineering.stackexchange.com/

There is also the Area 51 site for proposals for new sites: https://area51.stackexchange.com/