Form authoring in formhub is based on the XLSForm standard. While there is an initial
  learning curve, we’ve found that XLS provides a great interface for authoring forms — whether it’s
  simple 5 question questionnaire or a complex survey with hundreds of questions. XLS also makes
  sharing and collaborating on forms easy. Whether you need help authoring your first form or want
  to pick up advanced tips, please check out our 
XLForm Syntax page and
  our gallery of sample forms on 
formhub University.