Cesium is a free and open-source fork of sodium, which allows you to change minecraft physics, and optimize minecraft as well as sodium.
You can build from sources (./gradlew build or gradle build), or download a release.
You will need to install JDK 8 (or newer, see below) in order to build Cesium/Sodium. You can either install this through a package manager such as Chocolatey on Windows or SDKMAN! on other platforms. If you'd prefer to not use a package manager, you can always grab the installers or packages directly from AdoptOpenJDK.
On Windows, the Oracle JDK/JRE builds should be avoided where possible due to their poor quality. Always prefer using the open-source builds from AdoptOpenJDK when possible.
Cesium is licensed under GNU LGPLv3 (sodium too), a free and open-source license.