title_body: Are there any small scale auxlangs that are actually used by a substantial amount of people? International Auxiliary Languages are very, very ambitious, and probably bound to fail on a large scale. However, it seems plausible to me that there might be some corners of the world where an auxlang might be used to facilitate communication between more localized groups, much like English is used in many parts of Europe (and really, the world) for this purpose. But does this actually occur anywhere?
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).