About 2 years ago, the original macgap project stopped being maintained, so I'm happy to see that someone has forked it and maintaining it.
(This isn't an area i'm familiar with.)
Chromium Embedded Framework https://code.google.com/p/chromiumembedded/
Atom shell (based on CEF) https://github.com/atom/atom-shell
Brackets Shell (also CEF based) https://github.com/adobe/brackets-shell
node-webkit https://github.com/rogerwang/node-webkit
TideSDK http://www.tidesdk.org/
You can also apparently just roll your own if you want: https://github.com/lostdecade/web_view_example