You may think you've seen all the ways you can write a SQL query library, but Yesql is elegant and novel (AFAIK): https://github.com/krisajenkins/yesql
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Deno has the cutest PL mascot I think I've ever seen. Are there any other contenders?
Bril is a cute intermediate language for teaching (think simplified LLVM IR): https://www.cs.cornell.edu/~asampson/blog/bril.html
The idea of providing a standard JSON format to help students write basic passes is really elegant.
I've heard of 'blub languages', where you don't realise that other languages have better abstractions until you've experienced them.
I think the same thing happens with individual features. I've seen several C++ folks miss variadic generics in Rust, but I've not written enough C++ to feel it.