Playscii - Full-featured ASCII art and graphic editor and game creation tool
JavE - JavE (Java Ascii Versatile Editor) is a free Ascii Editor.
draw.io - Online diagramming application
asciiflow - Infinite ASCII diagrams, save to Google Drive, resize, freeform draw, and export straight to text/html.
UMLGraph - UMLGraph is a professional automated drawing tool that allows the designers the declarative specification and drawing of UML class and sequence diagram.
Charaster - Open-source ASCII art editor for browser-based, raster-style editing