This game is a great game to be played with physical cards and other people. However, there might be those times when no one's around to play with.
I've been looking for this game to play online for quite some time, but haven't been able to find it. Hence, I thought I might suggest it here.
A link to the game's rules can be found here: https://en.wikipedia.org/wiki/Sixty-six_(card_game)
Optimally, it would be nice if you could add different variants, such as the one I know best, called "Schnapsen", whose differences are listed under the link I posted above, but can also be found at https://en.wikipedia.org/wiki/Schnapsen
While sixty-six and Schnapsen are played with 2 players, there are also three- and four-player-variants available, which can be found at
https://en.wikipedia.org/wiki/Dreierschnapsen
for the three-player-variant, and
https://en.wikipedia.org/wiki/Bauernschnapsen
for the one with four participants.
I do not know any of the other versions listed on Wikipedia, but they might be worth having a look at as well.
It would be great, if you took this game into consideration or better yet, if you actually ended up developing it.

though i like dice games better, but well, i think they won't add this.

I think this game should only be added if we will also have one called thirty-three.

can't agree 77 much better.

Well, we do have ninety-nine, so... :P