Print the length of words as input as a histogram with horizontal bars
Looks good. There's really not a lot to review. About the only thing I can think of is that I'd like a little breathing space in the block, i.e.

{ |word| "*" * word.length }


But that's about it :)

Of course, there are also other ways to go about this, for instance:

puts gets.chomp.gsub(/\S/, "*").gsub(/\s+/, "\n")


Not that that's necessarily any better.