If there exists a business whose product is “scalable real-time order-book matching software” as licensed software or SaaS, I’d love to know about it! I’m in an adjacent space, and I’d love to strike up a partnership with such folks.
As far as I know, such a business doesn’t exist; all the big exchanges maintain their own core IP, much like all the big telcos in the 90s maintained their own core telecom-equipment IP. From what I know of the space, each player thinks that licensing the IP would just be either inviting a new player to the table, or more likely inviting enough new players to the table that other parts of the trading value chain would start to see value in abstracting-away and commoditizing their part of it.