tmux is a terminal multiplexer: it enables a number of terminals (or windows), each running a separate program, to be created, accessed, and controlled from a single screen. tmux may be detached from a screen and continue running in the background, then later reattached.
Screen is a full-screen window manager that multiplexes a physical terminal between several processes, typically interactive shells. Each virtual terminal provides the functions of the DEC VT100 terminal and, in addition, several control functions from the ANSI X3.
Zellij is a terminal workspace. It has the base functionality of a terminal multiplexer (similar to tmux or screen) but includes many built-in features that would allow users to extend it and create their own personalized environment.
abduco provides session management i.e. it allows programs to be run independently from their controlling terminal. That is programs can be detached - run in the background - and then later reattached. Together with dvtm it provides a simpler and cleaner alternative to tmux or...