The [arena runtime](./arena.ts) is just enough to make most language features work, but doesn't have sophisticated support for freeing memory. Useful when prototyping or for simple one-shot modules in that it produces very small modules with minimal overhead.
[No runtime](./none.ts) features at all. Useful for building low-level modules that do not require language features like managed classes, or if you'd like to compose your own runtime by including a custom memory allocator and garbage collector.
