Mathe: x = majors 1NT = minors others natural

Truscott: 1D/1H/1S/2C = natural x = clubs and hearts 1NT= diamonds and spades 2D = diamonds and hearts 2H = hearts and spades 2S = spades and clubs 2NT= both minors

Crash: x = Color (blacks or reds) 1D = RAnk (majors or minors) 1NT= SHape (round [hearts & clubs] or pointed [spades & diamond]) [also used against 1D response]

"DOBC" (similar to DONT): 1D = diamonds + other suit 1H = hearts + spades or clubs 1S = spades + clubs 1N or 2C = bad clubs x = one-suited (if clubs--- good) or big hand

No idea's whose but it's simple and good: 1D = both majors 1NT= diamonds