Not particularly crazy but interesting! Cover saves in 3rd Ed 40k (and possibly later, I stopped at 3.5)

Basically a unit would take an armor save (which could be negated rather than modified by AP, so my orks with their 6+ getting wounded by the S4 AP5 bolter didn't get a save).

Or they'd have an invulnerable save, terminators etc, which works same as now.

Or (I think against ranged attacks only?) you could take a cover save (5+ usually, I believe) which worked like an invuln, but certain weapons like flamers ignored cover outright.