Keyboard Maestro works across all applications. Many macros are general purpose (eg “Type my Email Address”). But also many are specific to a specific application (eg “Mark as Read” in Mail).
Typically you will create a Macro Group for an application, configure it to be active only when that application is at the front, and then place application-specific macros in that group. You can have more than one Macro Group targeting a specific application, and Macro Groups can target (or exclude) multiple applications (eg a Macro Group for Editors that includes macros like “Duplicate Line” that work in a variety of editors).
You can find some application specific macros in the Macro Library or on the Forum, as well as some applications listed below.