Yes and no. Roblox is free to download and play but has in-game purchases. These purchases are made with Robux, a virtual currency that you buy with real money. It allows you to buy in-game items and avatar accessories or to access certain games created by other users. On the other hand, Minecraft isn't initially free. You have to purchase the game to play it. The cost varies depending on the platform (PC, console, mobile). Once you've purchased it, you can play as much as you want without additional fees, and it does not offer any in-game purchases.