Almost five years ago, Saoirse "boats" wrote "Notes on a smaller Rust", and a year after that, revisited the idea.
The basic idea is a language that is highly inspired by Rust but doesn't have the strict constraint of being a "systems" language in the vein of C and C++; in particular, it can have a nontrivial (or "thick") runtime and doesn't need to limit itself to "zero-cost" abstractions.
What languages are being designed that fit this description? I've seen a few scripting languages written in Rust on GitHub, but none of them have been very active. I also recently learned about Hylo, which does have some ideas that I think are promising, but it seems too syntactically alien to really be a "smaller Rust."
Edit to add: I think Graydon Hoare's post about language design choices he would have preferred for Rust also sheds some light on the kind of things a hypothetical "Rust-like but not Rust" language could do differently: https://graydon2.dreamwidth.org/307291.html
Not sure if this is what OP is seeking, but I would be fine to have borrow checker removed, replaced with Garbage collector like Go/Python in such a language.
To build prototypes, I don't want to fight with borrow checker and neither I care for efficiency much. But I do want the macro system, traits, lazily asynchronous runtime, cargo like package manager, easy build system, etc.
Rust has so many powerful features, but only because of borrow checker (IMO) we can't use it for rapid prototyping like Python. With that replaced, this subset of Rust would be something which can be a great contender to Python/Go, etc.
The borrow checker handles more than just freeing allocated memory, it will also prevent data races and invalid concurrent access aso. I personally don't have any issues with using garbage collected languages, but the fearless concurrency is nothing I'm willing to give up.
Oh, I agree.
My worst experiences with Python are related to running multiple processes of which share anything. Rust was far easier in that.
Looks like interpreted Rust would be my only demand for Rust to shine in prototyping world.