Picom is a compositor for X, and a fork of compton (stuff will
retain the original name inside the package).

Out of frustration with the low count of standalone lightweight
compositors, picom was forked from Dana Jansens' fork of xcompmgr
and refactored. Bugs were fixed and features were added.

*NOTE* when upgrading between different versions you might find
that some options have changed values or have been deprecated or
removed and picom fails to start: launch "picom" from a console,
watch the error messages and edit your ~/.config/picom.conf
accordingly (or start from scratch with a new one, if you prefer)