This document consists of three sections:

Platform
  The JUnit Platform serves as a foundation for launching testing frameworks on the JVM. It also defines the TestEngine API for developing a testing framework that runs on the platform. Furthermore, the platform provides a Console Launcher to launch the platform from the command line and a JUnit 4 based Runner for running any TestEngine on the platform in a JUnit 4 based environment.
Jupiter
  JUnit Jupiter is the combination of the new programming model and extension model for writing tests and extensions in JUnit 5. The Jupiter sub-project provides a TestEngine for running Jupiter based tests on the platform.
Vintage
  JUnit Vintage provides a TestEngine for running JUnit 3 and JUnit 4 based tests on the platform.

Already consulted the JUnit 5 User Guide?