The mark ring. The kill ring. Registers. Each kind has its own use. Painless keyboard macros. Name, save, edit, insert a counter, make them yours. Dired. Wdi

The mark ring. The kill ring. Registers. Each kind has its own use. Painless keyboard macros. Name, save, edit, insert a counter, make them yours. Dired. Wdired. The find-*-dired functions. Org-mode. Tramp. These are all built in. Beyond that: a major mode for pretty much any language you can think of. Packages like magit and expand-region also immediately come to mind.