draw.io - Online diagramming application
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.
Adobe XD - Adobe XD is an all-in-one UX/UI solution for designing websites, mobile apps and more.
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project
DWGFREE - DWGFREE is an online platform that comes with a comprehensive collection of CAD blocks that can be downloaded without the need for registration.
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.