@mima >Someone is also trying to do a free reimplementation nof EoSD's engine in Python
That could be free software if EoSD's engine doesn't have scripting support, or the scripts have been replaced.

According to Arch AUR the license is "GPL3", but as the source repo is down, I can't check if that's GPLv3-only or GPLv3-or-later.

>fully reverse-engineered source is libre enough to you
Decompiled source code of proprietary software is not free software, as that's a derivative work of the binary and that binary is under a proprietary license.

Also, the result of such process is usually illegal to distribute - although there's little chance of ZUN suing in this case.

The README of the de-compiled sources repo say the license is "GPL2", but it's unclear if that's GPLv2-only or GPLv2-or-later and that is clearly not the license of most files ("hex rays" has even claimed copyright of de-assembler output, under no license, for example; https://github.com/nmlgc/ReC98/raw/master/th04_zuninit.asm).

https://www.gnu.org/licenses/license-list.html#NoLicense