The computer becomes the router. Its the software that makes a router. Check out the docs, its def not for everyone, but if you like having full control over your LAN without breaking the bank, this is it. I don't need a captive portal, but now its an option lol
Used to be you'd flash tomato or ddwrt onto your router, but you have to have specific routers and you chance bricking. Might still be an option, haven't looked into it in a while.