Simplicity? Modula-3 was simple, fast, and safe. PreScheme was less type-checked but powerful and simple. You can learn how to use them in a day coming from an imperative or functional language. Rust looks like it gives users extra power/safety with quite a bit of a learning curve (most say weeks to months) due to extra complexity. Definitely not simple, though.
https://en.m.wikipedia.org/wiki/Modula-3
https://en.m.wikipedia.org/wiki/PreScheme