The most depressing shopkeeper simulation in all of human history, Cart Life, is now available for purchase on Steam. It's a dirt cheap game which will almost certainly challenge, frustrate and depress you with its morose tales of people working themselves to death, only to scrape by.
It's only $5 normally, but it's being introduced at a 30% discount for a limited time. I guarantee you haven't played anything else like it before and highly recommend that you do. I love it, and I'm grateful it's arrived on Steam so that I'm more likely to remember to play again.