after 1M, 2NT is INV+ fit 4+. simple answers, 3M from both side reject invitation, anything else is (semi-)natural.
after 1m, 2NT is inv.
simple checkback after 1nt/2nt (with 2/3C, NOT the other minor)
inverted minor raise
strong jump shift (without competition) goldman/soloway/lawrence style. in competition, any jump shift is suit+fit inv+.
* drury-fit after 3rd position Maj opening