Userflows
UMLGraph
draw.io
Dia
yEd
OmniGraffle
CollabNet
UMLet
SnappCode
Duomly Backend Generator
Userflows
SnappCodeUMLGraph - UMLGraph is a professional automated drawing tool that allows the designers the declarative specification and drawing of UML class and sequence diagram.
Duomly Backend Generator - With Duomly Backend generator, you can build the complete backend & API solution with a few easy steps and no coding.
draw.io - Online diagramming application
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.
OmniGraffle - OmniGraffle is for creating precise graphics like website wireframes, an electrical system designs, or mapping out software class.