Discourse really isn't very good. If you want a more powerful forum system that doesn't need as much CPU power, get SMF or Xenforo or MyBB or something. If you want some new fancy thing, get NodeBB. Many of the sites that used to use Discourse are moving to NodeBB.
We don't see many NodeBB sites in the wild. If you want an old-schoool, traditional PHP / MySQL system, XenForo is a good choice, but there are a lot of critical security exploits, so stay up to date.
