There are a few things, the most important ones:

  - Including the tenant_id in modification queries as well (e.g. UPDATE/DELETE)
  - Support for specifying the current tenant as an ID (through `MultiTenant.with_id(123) { ... }`)
  - Helpers for multi-column primary keys in your migrations
  - Specific integration with Citus as a distributed multi-tenant data store (it'll just work without modifications)

I've considered contributing these back to acts_as_tenant, but it seemed easier to have a clean-cut, since the shared lines of code only ended up being about ~50 lines - mostly to set a default scope.