The roofs are hot, the sun is beating down, and you're standing with a cup of lemonade you need to prepare and sell for enough to get yourself out of debt. Lemonade Stand is a simulator of a small entrepreneurial dream from the nineties, when these things still made sense to teach without a computer and with a computer at the same time.

It's a simple economic simulator where you open a stand, buy ingredients, set a price, and wait to see how many people buy from you. The weather changes, temperature affects demand, and you try to hit the right balance between costs and price so you end up with more than you started with. The goal is to earn a certain amount over a set number of days or simply maximize profit.
Playing is a sequence of repeated decisions. Each day you choose the amount of lemons, sugar, and water, then set the price. The computer simulates sales based on the weather and your calculations. There's no graphics here, just numbers in text mode, no animations, just tables and records. The interface is clear, the way a DOS program should be — input, data, output. No frills.
Lemonade Stand taught the basics of trading before everyone on the internet started having fun with it. The game was played in schools because it works — it's simple, educational, and feedback-rich enough that you remember your mistakes. When you've gotten older and come back to it now, you'll find that the mechanics aren't complex, but they're not trivial either. A little intuition, a little luck.

Today you play it more out of sentiment or for the currently useful insight into how economics works. It's not a game for fun, it's an educational tool that pretends to be a game. It runs in a browser without problems, and if you want to understand why programmers in the nineties were obsessed with simulations of market behavior, it's a good place to start.