Is anyone using this? http://appimage.org/ Firejail will support it in their next update so you'd be sandboxing programs that aren't even installed on your box - which is pretty cool imo. There are a lot of prebuilt programs here - https://bintray.com/probono/AppImages
Mrkvonic just did a review of AppImage. Good concept in theory, its still a long way from being an easy to use installation system for Linux.