Is this a library similar to Quartz in Java for ruby?
There is nothing as complete as Quartz for Ruby. There is whenever a gem that you could integrate with one of the many frame job queues . Or, if you are willing to consider using JRuby, then you can fully integrate with Quartz directly.
Replacing Cron using a lengthy ruby ββprocess:
See Clockwork Ruby Stone. This gives a very simple DSL and runner.
If you need something more advanced, check out the Rufus-Scheduler gem. It looks like you will have to do some work to use this in a lengthy process, however it is much more powerful than the clockwork and supports EventMachine.