[Colex]

Devise does not impose anything on the number of tenants. I run a Rails app with multi-tenancy and SSO support with Devise. As someone has mentioned, although it does a lot of the work and it keeps well organized, you still need to do the UI for configuring and some backend logic.

[itake]

Devise doesn't support SSO, but it supports omniauth, which supports SSO, right?

You certainly can write and maintain code to add multi-tenant sso, but since omniauth does not support any configuration storage, you have to add that yourself.