draw.io - Online diagramming application
Zeplin - Collaboration app for UI designers & frontend developers
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.
avocode - Centralize design collaboration, version control, prototyping, feedback, and developer hand-off with Avocode. Work on any design, anywhere, with anyone. Sign up free ๐ https://avocode.com/.
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
Handoff by Marvel - Automatically turn designs into assets, specs and code