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.
FlowMapp - FlowMapp is a UX planning tool for creating visual sitemaps and user flow.
draw.io - Online diagramming application
A1 Sitemap Generator - A1 Sitemap Generator has been in active development and sold since 2005.
OmniGraffle - OmniGraffle is for creating precise graphics like website wireframes, an electrical system designs, or mapping out software class.
Octopus.do - Build your website structure in real-time and rapidly share it to collaborate with your team or clients. Start prototyping websites or apps instantly.