Sciter [1] is kind of a really lightweight electron. It's about 8Mb, cross platform, and you can either run it standalone (like electron) or use it as a library from Rust/D/Python/C#/whatever. You pay for the small size with a lack of compatibility with the existing Javascript ecosystem. Any moderately complex JavaScript library that interacts with the dom will probably use something that Sciter doesn't implement, so you end up reimplementing stuff like graph libraries. On the other hand there are a couple of very useful additional APIs that regular browsers don't have (like SQLite, control over window borders, transparent windows etc).

1: https://sciter.com/