Capistrano is a remote server automation tool and it's currently in Version 3. Version 2.0 was originally thought in order to deploy RoR applications. With additional plugins, you were able to deploy non Rails applications such as PHP and Python, with different deployment strategies, stages and much more. I loved Capistrano v2. I have used it a lot. I developed a plugin for it.
Capistrano 2 was a great tool and it still works really well. However, it is not maintained anymore since the original team is working in v3. This new version does not have the same set of features so it is less powerful and flexible. Besides that, other new tools are becoming easier to use in order to deploy applications, such as Ansible. More Info »
So, I have decided to stop using Capistrano because v2 is not maintained, v3 does not have enough features, and I can do everything Capistrano was doing with Ansible. If you are looking for alternatives, check Fabric or Chef Solo.