Looka - Make a logo you’ll love with Looka Logo Maker.
draw.io - Online diagramming application
Canva Logo Maker - Create your own custom logos without having to hire a designer with Canva's impressively easy to use logo maker. Completely free, completely online.
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.
Logo Foundry - Logo Foundry is a professional Logo Design Suite App for Android and iOS that let's you create professional branding for your business in Minutes.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.