There are no book orders; OpenPredict uses an automated market maker, and you can view the solana contract code inside the git repo here. We use constant function market makers, like manifold and uniswap. Curious to know if there's any benefit in selecting one vs the other, though.
Omen.eth appears to me to be offline; the other ones linked under azuro.org seem to be exclusively for sports betting and don't allow you to create markets. Augur also apears to have been abandoned & turned off as well, for some time; at the very least I and certain other users are getting the "Augur is not supported in your region" notification no matter which IP address we attempt to use, and the subreddit talks about it being dead, etc.
Which ones in particular were you referring to? I meant Ethereum mainnet specifically because the transaction fees are 100,000x what you pay on Solana.
My current understanding is that there aren't any. We have looked into all the ones that claim to do this and they are either currently offline, or never released, or require paying ETH's gas prices, or don't provide a public interface for trading, etc. etc.
For all of the people who like these odds, I've created a secondary prediction market about this bet, so you don't have to try to send Eliezer money.
This tutorial is now obsolete; no need to hold SOL or juggle between SOL and SOL-usdc to use the exchange anymore. Any transaction fees are just paid for by the node operator.