I was surprised by the ease of use of libflate when decompressing a gzip'ed file:
fn main() {
let mut file = std::fs::File::open("file.gz").unwrap();
let file = libflate::gzip::Decoder::new(&mut file).unwrap();
do_something_with(file);
}
And that's it, file is now like a normal file!
Another module I used for the first time is regex, which seems to have such a well-designed API actually.