Which Coin I could clone to create a potentially non worthless app coin?

I have an app, users receive worthless points as a way of rewarding experience.
You cannot do anything with that, I could sell a premium user thing, but I don’t like the idea.

I thought of creating a crypto coin, so I just have to mine, and give away all coins mined to the users, and that’s more interesting.
It might be as worthless as the virtual points, but just the possibility makes it more fun.

I believe the future is in proof of stake, Etherum is going there, bitcoin I think would go there if it wants to be a technically usable payment system etc.

So what PoS or similar coin I can go on Github, clone, change a few things, and start mining?
Is there one that does not store the whole transaction history? Simple, usable, lightweight.

I guess this might be seen as “polluting” the crypto world, but keep in mind I’m not going to announce it anywhere else than my app, it would be an internal fun project, will go nowhere, but in case it went out there, it would be only because of external interest.