LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
AT-UI - UI library for developing powerful web interfaces
draw.io - Online diagramming application
Remake - A way to make web apps with just HTML & CSS
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.
Sketch Extensions - An official collection of Sketch extensions & plugins