Fountain was originally designed as a screenplay format, but it actually works well for any text involving scenes and characters. Antony Johnston describes how he uses it for comics:

Turns out that, despite being designed for screenplay format, Fountain actually works pretty well for comics “out of the box” (note: there is no box) by using some of the built-in “forced format” syntax for underlines and emboldening.

To get you started, Johnston includes the templates he uses.

Fountain is flexible enough that you can also use it for stage plays and musicals. (We’re likely going to add a Lyrics element to the spec to help with the latter.) Ultimately, it’s up to individual apps to support specific templates, but the goal as always is to let writers create in any editor they love.