Arc vs Hack: What are the differences?

Arc: A dialect of the Lisp programming language developed by Paul Graham and Robert Morris. Arc is designed for exploratory programming: the kind where you decide what to write by writing it. A good medium for exploratory programming is one that makes programs brief and malleable, so that's what we've aimed for. This is a medium for sketching software; Hack: A programming language for HHVM that interoperates seamlessly with PHP. Hack provides instantaneous type checking via a local server that watches the filesystem. It typically runs in less than 200 milliseconds, making it easy to integrate into your development workflow without introducing a noticeable delay.

Arc and Hack belong to "Languages" category of the tech stack.

According to the StackShare community, Arc has a broader approval, being mentioned in 7 company stacks & 6 developers stacks; compared to Hack, which is listed in 8 company stacks and 3 developer stacks.