bulletphysics/bullet3 is the official C++ source repository for the Bullet Physics SDK. It provides real-time collision detection and multi-physics simulation (handling several kinds of physical models within a single simulation) for VR, games, visual effects, robotics, and machine learning. The latest release version is 3.25.
The repository contains the Bullet sources for real-time collision and dynamics computation alongside the PyBullet sources, which are Python bindings, and the repository's language listing is C++. The README recommends using PyBullet for robotics, reinforcement learning, and VR, and states that it can be installed with pip3. Simulating robots and physical systems is the purpose of this repository. The repository was created on April 12, 2011 and has 14804 stars. The license listing is unconfirmed, but the README states that source code without a separate notice follows the zlib license.
However, what changed in 3.25 has not been confirmed. It is unknown whether performance improved, whether the API changed, or whether examples or documentation increased. It is hard to gauge the scale from the version number alone. If you already use it, you can check the 3.25 changelog and then decide whether to upgrade. If you are seeing it for the first time, you can start with the PyBullet installation path described in the README. Until the 3.25 changelog is checked, it is difficult to treat this version as evidence of the latest features.