[LeonM]

Like many doom/quake clones (before ID released the source) I expect openage to be supplied without the artwork, you will need an original CD/image for that.

[alexpeattie]

Yep, the assets don't ship with the codebase - you need to provide your own original AoE II (or AoE II HD) installation.

[sleepychu]

Where does a designer stand if they want to make the missing resources so that the whole game can be shipped for free?

[JustinAiken]

Doom's done it - https://freedoom.github.io/

[taneq]

You can make anything you want, just don't use any copyrighted work without the copyright-holder's permission.