What are some alternatives?
When comparing asciiflow and Marvel, you can also consider the following products
Charaster - Open-source ASCII art editor for browser-based, raster-style editing
Invision - Prototyping and collaboration for design teams
Playscii - Full-featured ASCII art and graphic editor and game creation tool
Axure RP - The prototyping and specification software used by 87% of the Fortune 100. Beyond mockups, design interactive prototypes for business solutions, websites, and applications.
Ascii Generator 2 - Ascii Generator 2 (Ascgen2) is an application to convert images into high quality ASCII art - text...
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.