Three matches running at the same time: the front nine, the back nine, and the full eighteen. Lose the front and there are still two games left.

Front nine, back nine and overall are scored separately and settled separately.
A player can lose the front, win the back and still take the overall. Nobody is out of it at the turn.
Most groups allow a press: fall two down and open a new side match from that hole to the end of the nine.
Three simultaneous states is where paper scorecards give up. Still You shows all three — plus any live presses — on one screen without turning it into a spreadsheet.
Every one of these is a setting in Nassau — set once for the group and reused every round.
Automatic at two down, optional, or off entirely.
Same as the parent match, or half.
Full allowance, percentage, or off the low player.
Equal to the nines, or double.
The oldest side game in golf, and still the fairest way to keep a bad front nine interesting.

Beta groups get all six modes from day one. Four to a group — bring your regulars.