The FOS - Notifications dynamic action plug-in is built on top of a custom Javascript library and allows you to show success and error messages, as well as additional info and warning message types. It matches the look of native APEX success/error messages, and can be styled to your liking through Themeroller.
Using this dynamic action you can show multiple messages of each type, customize them by setting their icon, position, how they are dismissed, and more.
You can derive the message using static text with substitution support or from a Javascript expression or function. You can use HTML in the message or escape HTML for tighter security. You can see a wide range of examples below: