Trumpet is a mostly typical whist-like trick-taking game. The difference is that for most of the game, every card is a trump of some kind!
There are six suits numbered from 1 to 11 and three 'super trump' cards that beat all others. The game begins with no trumps at all; when a player wins a trick their counter moves forward one square on the board. The board is essentially just a scorekeeping mechanism. Pieces skip over occupied squares so it is quite easy to go from last to first with judicious play of cards and a little luck. Whenever a player's piece lands on a square marked 'choose trump', that player picks one of the six suits and nominates that suit as trumps (there is a ladder area on the board for documenting what suits are trumps). Play then continues until another player lands on a 'choose trump' square, and then one of the remaining suits is chosen to act as an even more powerful trump than the first. This goes on until all six suits have been chosen in an ordered ranking of trumps. Now landing on a 'choose trump' square entitles you to switch two suits on the ladder.
What this means for game play is that there is little point in holding on to cards of the highest trump suit, because they may not remain high for much longer. It forces you to play differently than in most fixed-trump games like Bridge or Mü, to get your cards out early while they are still worth something. Because of the occupied-square-hopping rule, it is also sometimes advantageous to give an opponent a trick so that you can then leap over them onto a 'choose trump' square (and deny them the opportunity at the same time).
At the time of its introduction, Trumpet was a novel take on the somewhat dull trick-taking genre of the day. Even now it is interesting and still worth a try.