Is ECWolf GitHub free?

Yes. ECWolf GitHub is released under Community / External hub and costs nothing. Neither it nor Wolfenstein has any paid content.

What do I need to run ECWolf GitHub?

Wolfenstein, which is itself free. ECWolf GitHub is an add-on and will not run standalone.

The PlayBound Launcher installs it in one click from Wolfenstein's mods list. You can also install it by hand — full steps are on this page.

Roughly 40 MB, on top of the base Wolfenstein installation.

Yes. The source is published at github.com/ECWolfEngine/ECWolf under Community / External hub.

ECWolf GitHub — Free Wolfenstein 3D via ECWolf Mod · PlayBound