draw.io - Online diagramming application
Viral Loops - Viral Loops is a viral and referral marketing platform to launch ranking competitions, sweepstakes, pre-launch and referral programs.
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.
Referral Candy - Run a fully automated, customizable and easy to integrate referral program for ecommerce.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
UpViral - Referral marketing platform enables anyone in running effective and profitable viral marketing campaigns – in minutes.