Playscii - Full-featured ASCII art and graphic editor and game creation tool
PabloDraw - PabloDraw is an Ansi/Ascii text and RIPscrip vector graphic art editor/viewer with multi-user capabilities.
draw.io - Online diagramming application
REXPaint - REXPaint is a powerful and user-friendly ASCII art editor.
UMLGraph - UMLGraph is a professional automated drawing tool that allows the designers the declarative specification and drawing of UML class and sequence diagram.
asciiflow - Infinite ASCII diagrams, save to Google Drive, resize, freeform draw, and export straight to text/html.