GENERALS this is our mission ...
.
.
happy modding Generals:D Life is short

we need that a free SAGE engine ...:D
.
.
and the engine called " MODDER ENGINE " who wants to join ..:D GENERALS

---

Start learning to program, doesnt matter what language, preferably C++, Java or maybe even Haskell.
Make a lot of 2d games and learn how stuff works and if you have mastered programming which will take a few years then you will spend at least 3 years on programming an 3d engine like SAGE.
It is not open source because a whole team of people worked on it and all those people had to feed themselves and their families.
Learn how to program and gather people around you who also spend their freetime with programming, try to find people who are good with graphics and such and maybe just maybe you will succeed...
People like Linus Torvalds are reaaaaally hard to find, he implemented Linux all by himself, he is in a league of his own...

And btw, the SAGE engine is pretty modder friendly, i suggest that you spend some more time on modding and discover it yourself...

Greetz

---

Just like a person who made DOS

.
.
Sir DOS now is opesource ..:D
.
.
https://www.wired.com/2014/03/msdos-source-code/ 
.
.
CHEERS ...:D

---