The hosted version is set up to do Travis CI, like the defunct homu.io was, but you can configure it to do anything that uses Github Status to report when it successfully builds a branch (AppVeyor and Circle CI, for example, should work). It can't do more than one, though.
The source code is all on Github.
Cool. Other than the fact that the hosted homu version is dead, (the servo fork is maintained too,) how does this currently compare to homu?
Edit: It being written in Rust is certainly a nice plus.
I'm looking forward to use it for imag (github) - though I wait until this is stable.
BTW: I'm getting a "Bad Gateway" when clicking the link for the hosted site.
Am I correct that this evolved into https://bors-ng.github.io/? Is bors-ng ready to use, or is it still in an experimental phase? I am thinking about using some bors offspring for https://github.com/intellij-rust/intellij-rust 
Your interpretation of the situation is correct. Aelitabot.xyz is going away in about a month.
As for whether Bors-NG is experimental, that really depends on how you define "experimental." I've committed to the interface (bors.toml, bors r+, etc) enough that there won't be regular breaking changes, but due to #64 I wouldn't recommend for rust-lang/rust to move over to it yet.