There is now a new Zero-K lobby, I hope that auto-upgrade worked well on your system :)
This new version also works on Linux and should work on Mac with little tweaks.
To install on Linux, run something like that:
sudo apt-add-repository ppa:spring/ppa
sudo apt-get update
sudo apt-get install spring mono-complete xprintidle p7zip wget
On Windows there is now a new feature to use external browser instead of built in, and lots of little tweaks.
Both platforms now share identical executable and self update at the same time.
Unfortunately that means I had to strip some WPF vector visuals form ZKL, but they can now be recreated using bitmaps and manual rendering. So please hold on until I get some artist help :)
ZKL for linux wont be able to download engine 91.0 because it does not exist as a static build yet.
If you do have a working 91.0 for linux, make a symlink in .spring/engine/91.0/spring to make ZKL use it.