There is DBI and ActiveRecord. I am not sure if there are any other high level ways of connecting to a database in Ruby. DBI is a wrapper around DB drivers and ActiveRecord is similar except it provides a whole lot of functionality. It is part of Rails, but you don't have to use rais to use AR. What I like about AR is that in most cases you never have to write SQL code, which I despise.
"Computer science is no more about computers than astronomy is about telescopes" - Edsger Dijkstra