Very simple "Alt-Tab" / MRU (Most Recently Used) switcher for sway, requiring only bash, jq and sway itself, no daemon running.

sway-alttab.sh

#!/bin/bash
#
# Very simple "Alt-Tab" / MRU (Most Recently Used) switcher for sway,
# requiring only bash, jq and sway itself, no daemon running.
#
# Copy it somewhere in $PATH and add to ~/.config/sway/config:
#   bindsym --no-repeat Mod1+tab exec sway-alttab.sh
#
# or run in a terminal:
#   swaymsg "bindsym --no-repeat Mod1+tab exec sway-alttab.sh"

# The only possible argument is how many windows to skip (0-9):
#   0=no switching, 1=previous (default), 2=next-previous, ...
case "$1" in
    [0-9]) SKIP="$1" ;;
        *) SKIP="1" ;;
esac

CON_ID=`swaymsg -t get_tree | jq ".. | select(.type?==\"workspace\" and .nodes[]?.nodes[]?.focused?==true).nodes[].focus[$SKIP]"`

swaymsg "[con_id=$CON_ID] focus"