You're reading the documentation for a version of ROS 2 that has reached its EOL (end-of-life), and is no longer officially supported. If you want up-to-date information, please have a look at Iron.
Related Projects
Gazebo
Gazebo (gazebosim.org) and its predecessor Gazebo Classic are the first open source choice for 3D physics simulation of ROS-based robots.
Large Community Projects
Large community projects involve multiple developers from all over the globe and are typically backed by a dedicated working group (cf. Project Governance).
ros2_control (control.ros.org): Flexible framework for real-time control of robots implemented with ROS 2.
Navigation2 (navigation.ros.org): Comprehensive and flexible navigation stack for mobile robots using ROS 2.
MoveIt (moveit.ros.org): A rich platform for building manipulation applications featuring advanced kinematics, motion planning, control, collision checking, and much more.
micro-ROS (micro.ros.org): A platform for putting ROS 2 onto microcontrollers, starting at less than 100 kB of RAM.
Further Community Projects
The global ROS community develops and maintains hundreds of further packages on top of the core ROS 2 stack. Some of them come with their own websites for documentation. Your best entry point to discover these works is the ROS Index (index.ros.org).
Hint for developers: If you maintain a README.md file in the root of your package folder (which is not necessarily the root of your repository), this file is rendered into the overview page of your package at index.ros.org.
The file may be used for documenting your package and supersedes the package documentation pages in the ROS Wiki from ROS 1.
See the fmi_adapter package as an example.