So, you know how like Rails runs on Ruby, which is kinda slow. As you may or may not know, Ruby isn't compiled into any sort of machine code, or even bytecode. It is compiled down into a tree-representation (like all languages i think), but instead of taking this tree representation into bytecode or native machine code, they just leave it. This makes ruby extra slow and hard to optimize. Rubinus (as far as I know) takes the tree and makes bytecode which is then executed on a VM. This should make it much faster.