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Re:Push API – W3C Working Draft by DanBC on Monday October 27, 2014 @08:35AM (#8515081)
If you want free / open source you could look at Dia. http://dia-installer.de/index.html.en

You could also try yED. http://www.yworks.com/en/products/yfiles/yed/

EDIT: This site has a nice list of a bunch of software that you can check. http://alternativeto.net/software/dia/

Re:Push API – W3C Working Draft by grap on Monday October 27, 2014 @10:28AM (#8515594)
The list from your edit is great. I didn't even know that alternativeto.net existed.