Vectr is an app similar to Inkscape, Adobe Illustrator and Corel Draw. It's fairly new and I believe it's out of Beta already. I don't think it's open source, but it is a freeware on multiple platforms which even includes an online browser app. I'm not sure if it meets PortableApps.com's criteria for being converted into a portable app, but it's worth a look at least. The interface looks really polished and very nice to work with.
The website can be found here: http://vectr.com
Thanks for checking it out .