These could include MySQL, PostgreSQL, Redis, MongoDB or ElasticSearch for your databases or nginx and passenger or unicorn your web and application servers.
But what if you use a different type of server in your app that's not supported by Cloud 66? To take care of that, you can now fire up Custom Servers in your stacks.
A custom server is a server that has all the basic Cloud 66 features:
It shows up under your Stack, it is monitored and kept up to date by Cloud 66, secured by the firewall management and ActiveProtect and you can use the toolbelt to SSH into it just like your web and database servers.
As an example, you can use Custom Servers to host non Ruby parts of your app or deploy a middleware like ActiveMQ for your stack.