What happened to Freemind?

You might try Freeplane (sudo apt-get install freeplane). Freeplane is a Freemind fork from about 10 years ago that seems to be in more active development.

AnGus

You can still install FreeMind, and it still works great – in my case, under Ubuntu 18.10. It is no longer provided as a Debian package in the repositories, but as a distribution independent "Snap" package.

You can install it as follows:

1. Assuming you want the latest beta version, which I'd recommend, run this command to install the FreeMind snap (as documented here):

   sudo snap install freemind --edge
   

   You can now already start FreeMind via the desktop icons and menu entries of your desktop environment.

2. Add the following symlink to be able to start FreeMind from the terminal, Alt+F2 Run Dialog etc.:

   sudo ln -s /snap/freemind/current/freemind/freemind.sh /usr/local/bin/freemind
   

And if you want to uninstall it again:

sudo snap remove freemind