Hoare logic organized program proofs around preconditions, commands and postconditions, creating a compositional calculus that still shapes verification tools and software contracts.
Monitors moved mutual exclusion and condition synchronization into structured program modules, helping make shared-memory concurrency easier to reason about.
Tony Hoare's CSP made communication and parallel composition central programming concepts, influencing formal methods, occam and later channel-oriented languages.
Tony Hoare's Quicksort made partitioning the heart of sorting: rearrange data around a pivot, then solve two smaller sorting problems recursively in place.