Hammerspoon is free, but you have to write your automation scripts in Lua. If your comfortable with Lua this might be totally fine and give you a lot of flexibility.

Keyboard Maestro on the other side is commercial software with a nice UI editor were you can compose automation scripts by simply dragging and dropping actions. Personally I use Keyboard Maestro and find it absolutely worth its money. Even without any programming experience you can create powerfull scripts within minutes. I use it as clipboard manager, snippet manager, text expansion and much more.