Stack Exchange is the wider network of Q&A sites that Stack Overflow itself is part of, also run by Stack Exchange Inc. (Prosus). It ranks #5 among developer communities at roughly 46.5% usage share. It covers everything a pure coding site doesn't — math, physics, DevOps (Server Fault, Super User), and UX design — useful the moment a question drifts outside pure code.
Each topic in the network is its own separate site with its own domain, all sharing the same Q&A format and reputation mechanics as Stack Overflow. Knowing the naming pattern lets you jump straight to the right sister site instead of searching Stack Overflow and getting redirected.
# sysadmin / server config questions
serverfault.com
# general computing / software questions (not "coding")
superuser.com
# interface & user-experience design questions
ux.stackexchange.com
# search a specific sister site directly
serverfault.com/search?q=nginx+reverse+proxy+timeoutWhen a Stack Overflow question gets closed as "off-topic," the closing comment usually names the correct sister site to re-ask it on — that's a strong signal of exactly where the right community for that question actually lives.
One Stack Exchange account works across every site in the network, so if you already have a Stack Overflow login you're already set up. Browse stackexchange.com/sites to see the full list and pick sites relevant to your work beyond pure coding.
# typical first steps
1. Log in with your existing Stack Overflow account at stackexchange.com
2. Browse stackexchange.com/sites for the full network list
3. Bookmark 2-3 sister sites relevant to your stack (e.g. serverfault + ux)
4. Search the specific sister site before asking, same as Stack Overflow