Dia (dia-installer.de (Links to an external site.)) is a possible editor for ER‐diagrams and the one I use.
You are however free to use any editor you like!

Dia is freely available for Linux, macOS and Windows and should also be installed on the Chalmers computers in the labs.

Dia supports lots of different kinds of diagrams. To find symbols for E-R diagrams, choose ER from the menu in the tools panel.

Pro-tip: Double-click an entity/relation to set its properties (e.g. weak etc) ER-mode.
Pro-tip: Double-click an attribute to set primary key etc.
Pro-tip: Double-click a line to change arrows, the curved arrow is available under "more arrows".
Pro-tip: There are no ISA-relationships in the ER, but you can use merge/extract from flowchart (and just write ISA on them).
Pro-tip: Always connect lines to the points of diamonds, not their center.

If Dia doesn't show up this notes from a couple of year ago could be of help:

Go to your Applications directory where Dia.app exists (mine was located at: /Applications
Right click the icon and click on Show Package Content
Go to the directory Dia.app/Contents/Resources/bin
Edit the file dia, in your favorite text editor
After line 39, add the line: export DISPLAY=:0
Save and exit
Close XQuartz if its running
Now Dia should come up
If it does not come up, try restarting your computer

If not, try and add the line - export DISPLAY=:0 to your ~/.bash_profile, re-login and hopefully you should have Dia working once again.