It is important to note that Techland does not typically release the Chrome Engine 5 editor as a standalone, free download. It is usually bundled with the games that utilize the engine.
Check the box next to "Dying Light Developer Tools." Steam will immediately begin downloading the Chrome Engine 5 SDK. This package includes: Chrome Engine 5 Level Editor Download
You might think the Chrome Engine 5 Level Editor is limited to "mods," but the community has produced standalone-quality content. It is important to note that Techland does