I've never made any software for mobile phones, so this would be something different. And yes, I know that card games have been done on phones before, and on websites, but maybe there is some scope for new ideas here. The idea starts with the game of Jass, but of course if there's any appetite for the basic principles then it could be extended to other card games, or even other turn-based games.
Just using a pack of playing cards is simple, cheap, extremely portable, and of course doesn't require any charged batteries. So why would a mobile phone app appeal?
Maybe you want to play a four-player game but you don't have a suitable playing surface (you're on a plane, or in a wobbly bus, or reclining on beach loungers, or you're somewhere windy, or it's dark, for example). Maybe you hate shuffling cards, or you hate adding up the points yourself and want the phone to do it for you. Maybe you're still learning the game and want to switch on tips while you play.
Jass also can be played with different card faces, and if you have real cards then everyone has to use the same deck. With a mobile game, the four players can see their own cards and the cards played by the others in whatever style they choose. So if you're used to playing with French cards, you don't have to get confused when your friends want to play with the Swiss German ones.
The instructions on screen can obviously also be in different languages for different players.
It's possible that exactly this app already exists somewhere — in which case please let me know.
The reason I'm writing this is that there are some additional requirements which I believe are not met anywhere yet:
The way I see it working would be like this. One member of the group would purchase (at a reasonable cost) and install a "gamesmaster" version of the mobile phone app. This would be started first, and it would listen for bluetooth connections from nearby phones.
The other three members of the group would install (for free) a free version of the app which only allows them to connect to an existing game. They start this app, and connect via bluetooth to the first phone. Then each player selects where they are sitting in relation to the gamesmaster — this defines the game play order and the diagonal team pairs.
Then the cards are dealt (perfectly fairly shuffled), and the hands appear for each player the way they wish the cards to be represented (with selectable face sets). The phones make it clear to each player whose turn it is, provide tips or explanations as requested (the gamesmaster can choose what is allowed for each game) and in the requested language(s). Playing a card would be done by swiping upwards, at which point that card would appear in the centre of the table for each player (possibly appearing very differently for each player).
At the end of the game, the points for each team would of course be calculated automatically, with no mental gymastics or chalkwork necessary.
It would be possible to also introduce a kind of handicap system for groups of very mixed experience — I can very well imagine that having artificial help for some players and not others would not exactly be very popular, but it would be possible. Someone who has played Jass for years and is easily able to keep track of played cards has a big advantage over a complete beginner who is even unfamiliar with the cards. But if the beginner had a reminder what the current trump suit is and some kind of indicator for which cards haven't been played yet, then the advantage could be (temporarily) reduced to make the game more fun.
If you wanted, this help system could also help explain for example why that Nine just beat that Ten, even though usually a Ten beats a Nine (hint: because this Nine is the Näll), or why that Under just beat that König (hint: it's the Buur). Or it could show the score of each Stich as it's won, showing during the game which Stiche are most valuable and which team is currently winning. Again, this information isn't secret, but showing it during the game could help learning.
There's a lot about developing apps for mobile phones which is completely unknown for me. And this project would require not one but two separate apps. Probably it would have to be Android-only, and then you're looking at how many people in the World want to play Jass but not with cards. Possibly not that many. And any that do, probably already do it via online access, web tracking, advertising and all the rest. So it's probably looking at a serious time investment in order for a handful of purchases, where the prices are driven down to next to nothing. And then the megacorporations take a hefty slice of that too.
So I guess... probably not?