Philip Kaludercic has an interesting post on some little known functionality in core Emacs. One of the wonders of Emacs is the package system that can add practically any desired feature to Emacs. That sometimes means that we forget how powerful Emacs is out of the box.
Kaludercic takes a look at some of those features. His post considers:
autoinsert- This doesn’t do what you probably think and can be very useful if you write code.
htmlfontify- This does do what you think. As Kaludercic says, most people use it through Org mode.
package-x- This is useful for making local package archives.
type-break- Implements a light weight Pomodoro technique.
strokes- This allows you to configure mouse strokes to invoke a an Emacs command.
mode-local- A really convenient way to define variables that are active only in a prescribed mode.
shortdoc- A new, not officially released functionality that provides some useful documentation for Elisp programmers.
There’s a lot more detail in Kaludercic’s post so head on over to Kaludercic’s site to get the full picture.