Not open source but with a free tier: www.breakdown-notes.com.
Disclaimer: my project.
Ask HN: What tools do you use for creating diagrams?
11–14 of 14 posts
Re: Ask HN: What tools do you use for creating diagrams?
#12Using PlantUML.
http://plantuml.com/
Re: Ask HN: What tools do you use for creating diagrams?
#13Re: Ask HN: What tools do you use for creating diagrams?
#14I'm a fan of the web-based www.gliffy.com