GraalVM is a set of tools. It's hard to cover in one reply... The big feature is it's probably the most advanced JIT optimizing compiler available outside of research. It can run _a lot_ of different languages too and it's cross platform by default. It will literally run on any device that can run a JVM, and even some that can't. It's also written in a language (Java) that's far more accessible for people to make compiler enhancements too, hence it's meteoric rise.

Another big feature is it's Native Image feature, which is an AOT compiler. You can make a native executable out of a Ruby, Java, JS, or Python program, with some asterisks. I think Quarkus' benchmarks really speak to why this feature is valuable (scroll down on this page) https://quarkus.io