Snapcraft
One of the things I always liked with Ubuntu it is "A better Debian Unstable". Same package format and OS layout. A reasonable mix between new packages, and stability and QA.
Firejail
One big thing for me over the last few years is containers, security confinement and sandboxes. It's not a new thing, but in the Linux space a lot of interesting tooling around these technologies has appeared over the last years.