Playscii - Full-featured ASCII art and graphic editor and game creation tool
draw.io - Online diagramming application
PabloDraw - PabloDraw is an Ansi/Ascii text and RIPscrip vector graphic art editor/viewer with multi-user capabilities.
Nektony Mac Visio Viewer - Nektony Mac Visio Viewer is a fully featured application for Mac OS X operating systems to view MS Visio files.
REXPaint - REXPaint is a powerful and user-friendly ASCII art editor.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.