Serenity CE is licensed under the GNU General Public License version 3.
Serenity: Community Edition is an open-source release of the Serenity client for Minecraft 1.8. The source is near-untouched as of the initial commit, the only changes since the commercial b50 release being removals of phone-home functions such as the update notifier, and security features. Serenity: Community Edition has been released in place of commercial Serenity releases.
$ ./gradlew setupDecompWorkspace
$ ./gradlew genIntellijRuns
For OptiFine, use simpledeobf to deobfuscate OptiFine,
include it in the classpath, and then use the OptiFineTweakerDevWrapper followed by the SerenityCascadingTweaker tweak classes instead of the SerenityTweaker class.