Not a ruby shop here so it's not directly comparable, but I'm very happy with beanstalkd as a minimalistic job queue. We're on mysql for historical reasons, and it didn't support SKIP LOCKED at the time, so we had to add another tool.

I pulled beanstalkd into a legacy PHP/MySQL application several years back and was very pleased with it. It's probably not the right choice for a modern Rails application, but if you already don't have a framework, it's a straightforward solution to drop in.