There is also a website that allows people set a public bet, and people can arbitrarily bet for or against it. e.g. Bitcoin will be under $500 by January 01, 2021. It also covers practically any other bet, since the users are actually the ones that set the markets.
Forgot what the website name is though.
Whoever manages to find it and posts it will get 1 merit. (PM me so I see it).
Following up with this, I managed to remember the site, it's called predictious;
https://www.predictious.com/
I've never used it, but it basically describes the feature that OP mentioned.
There's a few interesting bets on there though, and there are bets in five categories:
Sports
Politics
Economics
Entertainment
Science & Tech
I'm not a fan of how the system works though, so won't be trying it myself.