PredictIt had a limit of $850 on the platform, and even it's in the process of being shut down by the CFTC. I see it as a chicken-and-egg problem because having actual stakes even when miniscule means that smarter decisions are made with allocation; but I feel a lot of users would grow bored or not even use the platform if they could only use play money. My personal favorite example was ran in Popular Science magazine[0] for a few years where users could buy/sell imaginary shares based on the % probability outcome of certain events/discoveries being made by a specified date.

[0] https://en.wikipedia.org/wiki/Popular_Science_Predictions_Ex...