draw.io - Online diagramming application
M+ 1m - Download and install the M+ 1m free font family by M+ Fonts as well as test-drive and see a complete character set.
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.
Inconsolata - OSX, Productivity, Design, Typography, powerline, and Fonts
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Bitstream Vera Sans Mono - Bitstream Vera Sans Mono Font | dafont.com