I have fixed the popup window saying that you cannot reach the web server, even if you choose to use Docker.

By the way, you have to start Assemble2 from the command line, using one of the launch scripts (./launch_Assemble2_for_MacOSX.command for example). If you double-click on the jar, Assemble2 will not get the shell PATH and then will not be able to find Docker.

Enjoy!