AASM is a continuation of the acts-as-state-machine rails plugin, built for plain Ruby objects.
Workflow is a finite-state-machine-inspired API for modeling and interacting with what we tend to refer to as 'workflow'. * nice DSL to describe your states, events and transitions * various hooks for single transitions, entering state etc. * convenient access to the workflow specification: list states, possible events for particular state
There are many finite state machine implementations for Ruby, and they all provide a nice DSL for declaring events, exceptions, callbacks, and all kinds of niceties in general. But if all you want is a finite state machine, look no further: this has less than 50 lines of code and provides everything a finite state machine must have, and nothing more.