I already recommended Amun-Re and I'll stand by that one.
Basically all of his auction games are good, except Strozzi. Strozzi feels like a parody of a Knizia game. The scoring system is typically interesting like most Knizia titles, but absolutely nothing else about the game is interesting at all. The auction mechanic belongs in a 20 minute filler and does not stand up to 3 long rounds of play.
Medici is a lot of fun and has a lot of play to it for a single mechanic game. The valuations are so damned opaque at first and the second you get used to them the relative values of everything changes and you have to figure it all out again. Medici scores often vary wildly as players struggle to make sense of the system and it stands up to repeated plays extremely well. Whether you are bidding too low or too high, you are pretty much always doing it wrong, but if you do it less wrong then everyone else you might just win by 20 florins. Its a very fun game. Best with 6
Stephenson's Rocket is Knizia's thickest game, where you have three different types of pluralities to manage. Obviously you can't be ahead in everything, so the trick is to manipulate the situation so that your pluralities are worth more, but of course the only way to do that is to make sure the other player's actions help your position. This ranges from subtle decisions on where to concentrate resources and being able to predict where mergers will be forced, but it also comes through the blunt force of the veto mechanic. This is a no hidden information, no random element fight for inches and it is excellent, but not something that really has much casual play appeal. Best with 4
Quo Vadis? is a pure negotiation game and probably the best one ever made. It plays in under an hour (unless you have some very stubborn/slow negotiators) and cuts to the chase without any extraneous mechanics: if you get a majority of votes in a room, you move to the next room and get points. The struggle to make it to the last room vs. the struggle to get enough points is delightful and the extra bargaining chip of the Caesar token ensures that no one will have a dead turn. I love when the bonus chips run out and the game gets super serious as all of the margins instantly turn razor thin. Some people don't like negoiation games inherently, but if you even sort of like the idea of them, this game fixes a lot of the problems the have, which is ironic because it was one of the first. Except for Diplomacy of course which came out 34 years earlier, but that's a monster game that can take over 5 hours. Best with 5
I have no idea if any of those games have an App, but Samurai does and its a very fun game too. Super strategic, best with 2 players.