Bocker – Docker implemented in around 100 lines of Bash (2015)
Until well into the 2000s we deployed all our services as chroots. I even sold a server side product successfully which was distributed as chroot so it would install almost on any Linux distro without having to care about dependencies. It worked really well and felt quite a bit more accessible and lighter than docker. We just had a script which basically did:    wget https://bla/image.tgz
    tar xzf image.tgz
    rm image.tgz
    chroot image/start

and the product would be installed and up & running. A lot of clients thought it was magic. No Apache install? No MySQL install?? It works on Fedora & Centos & Debian & Ubuntu & ... ?I use this currently still a lot to run new software on unsupported hardware/kernels. For instance, I run a lot of new (Ubuntu) software on my OpenPandora under the default OS on that device; I have an SD with a chroot with Ubuntu and things like dotnet core. Runs fine. Gives devices like that a second youth.