(full disclosure: I’m a co-founder of Discourse)
Hosting is our core business at Discourse. The software is available for free, but its current pace is sustained by our hosting plans. By going with us you are directly helping us fund development and making it better for everyone else who uses it!
Technically speaking, we host all our customers on dedicated bare metal servers for performance. Our response times are considerably higher than cloud environments due to lack of virtualization which has a particularly bad penalty on Ruby applications.
We have built in quite a lot of redundancy to this set up. No customer runs on a single server regardless of plan. Everything is spread out to avoid hardware failures and for extra speed.