On a rooted Samsung Galaxy S4 (SGH-M919 aka jfltetmo) running Cyanogenmod 11, how can I remap the leftmost hardware button so it brings up the recent apps list?
This is pretty easy to do.
Just go to
Settings->Buttons and scroll down to
Menu button. Below that you see
Short press action and you can select your preferred action (Recent apps switcher in your case).
That's it. Depending on the developer of the ROM you may be able to remap other buttons as well.
you can enable the s4 ithink s3 also , the BACK button for recent tabs buy touching it for 1-2 seconds ( in the accessibility setting)
that serves the same