I haven't found a reason to try it yet, but:
https://horizon-eda.org/
Or maybe KiCad.
Or maybe KiCad.
LibrePCB is also worthy of note and seems aimed at Eagle users. Also fundamentally more modern and solid than kicad.
What I am missing from HorizonEDA is the ability to set constraints to signals/pads such as maximum and minimum current, voltage, frequency or setting impedance targets.
There is also no easy way to do a simple static current FEM simulation on custom polygon shapes. You can already do this using a chain of four open source tools but it is a lot of manual steps.
You can set a net or net class to have a set of geometric constraints suitable for a particular impedance or current or voltage. This matches or surpasses the capability of every other EDA software that I've used.
I also think it's unreasonable to ask EDA software for a full on FEM simulation. You wouldn't want to do that with the full board geometry anyhow.
During that time I created roughly 10 finished (and working) projects using the software.
The only downside compared to KiCAD is that the official parts library is smaller. But what is in there goes through a review process and is often verified by other builders. There are also fancy things like 3D views, length tuning, alternate footprints, board layouts consisting of multiple boards, ...
If you are one of the people who has no problem creating their own footprints and always wanted to like KiCAD, but is driven insane by the UX, this one might be it.
I run it both on Windows and Linux and it works fine. The only thing it does not run on (as of now) is OSX, because of some GTK-issue, but once that is resolved there is no reason why it couldn't.