PGF and TikZ - PGF/TikZ is a tandem of languages for producing vector graphics from a geometric/algebraic...
Playscii - Full-featured ASCII art and graphic editor and game creation tool
LaTeXDraw - LaTeXDraw is a graphical drawing editor for LaTeX.
draw.io - Online diagramming application
Diagrams Haskell package - Diagrams is a powerful, flexible, declarative domain-specific language for creating vector...
UMLGraph - UMLGraph is a professional automated drawing tool that allows the designers the declarative specification and drawing of UML class and sequence diagram.