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Check out Dylan and Sweet Expressions.

The Arc language wiki has this list of languages that make use of significant whitespace.

https://sites.google.com/site/arclanguagewiki/more/list-of-l...

See this: http://readable.sourceforge.net/

Works with both Scheme and Common Lisp, two most popular Lisps out there. Nobody uses it because paredit/parinfer is just too convenient, but the option is there.