Little Big Adventure 1 and 2 are two classic titles originally developed by Adeline Software International and now they've both had their engine source code officially released. They're now available under the GPL license that you can see on GitHub (#1, #2).
Publisher [2.21] announced back on October 8 that a new Little Big Adventure game is on the way, with no other information. Since then they've posted a few other bits, including the decision to use Unreal Engine for the next-generation game. Today though, October 27, they announced a surprise with the source release mentioning "Our objective is to preserve those pieces of technical mastery and true groundbreaking vision. We also want to give back to the LBA community who kept cheering on the games during all those years.".
Each game has two code repositories, one where only they and ex-Adeline developers will contribute and one dedicated to the community for pull requests. They further note that "this code was never meant to be seen by anyone outside the Adeline Software team. The source we are releasing is mainly untouched (only the developers names were removed) including bad french, variable names in “frenglish” and some comments that are just too funny not to share".
The engine source code may be open source but like a lot of projects that do this, the rest of the assets are not so you still need a copy of each game. You can find them on: