The Panda3D SDK contains development libraries for users who wish to develop applications with the engine. Everything that is needed to work with the engine is installed with this package.
The source code for Panda3D is hosted in a Git repository at GitHub. This is where the latest version of the source code is available.
The Panda3D Runtime package provides all the functionality to run Panda3D applications both standalone and in the browser. This was the recommended download for users who just want to run Panda3D applications and do not intend to develop with the engine, but it will be discontinued soon.