title_body: Are there any small scale auxlangs that are actually used by a substantial amount of people?
upvoted_answer: The line between "conlang" and "supradialectal standard" can get incredibly fuzzy. You mention Rumantsch Grischun and Modern Hebrew yourself, something along similar lines, but much more successful in terms of number of speakers is Bahasa Indonesia. Any number of other supradialectal standards depending on how strict you are with drawing the line may fall under this category.
  
  In addition to supradialectal standards, another thing that may or may not be considered a conlang is controlled languages, such as ASD STE-100 Simplified Technical English which see some use in various technical documents (but aren't really spoken).