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?

All Modules Jupiter Vintage Platform 
Module Description
org.junit.jupiter
Aggregates all JUnit Jupiter modules.
org.junit.jupiter.api
Defines JUnit Jupiter API for writing tests.
org.junit.jupiter.engine
Provides the JUnit Jupiter TestEngine implementation.
org.junit.jupiter.migrationsupport
Support for migrating from JUnit 4 to JUnit Jupiter.
org.junit.jupiter.params
JUnit Jupiter extension for parameterized tests.
org.junit.platform.commons
Common APIs and support utilities for the JUnit Platform.
org.junit.platform.console
Support for launching the JUnit Platform from the console.
org.junit.platform.engine
Public API for test engines.
org.junit.platform.jfr
Provides the JUnit Platform Flight Recording Listener.
org.junit.platform.launcher
Public API for configuring and launching test plans.
org.junit.platform.reporting
Defines the JUnit Platform Reporting API.
org.junit.platform.runner
Runner and annotations for configuring and executing tests on the JUnit Platform in a JUnit 4 environment.
org.junit.platform.suite.api
Annotations for configuring a test suite on the JUnit Platform.
org.junit.platform.testkit
Defines the Test Kit API for the JUnit Platform.
org.junit.vintage.engine
Provides a TestEngine for running JUnit 3 and 4 based tests on the platform.