Custom packages
core and world (see Available packages) cover the packages ps2build update installs for you. Anything else - a library you wrote, or a third-party project someone else maintains - installs as a world package the same way.
Installing one
Download the package's release zip and extract it to $PS2DEV/packages/world/<name>/, matching the name: its package.yaml declares. For example, ps2gl's release zip extracts to $PS2DEV/packages/world/ps2gl/. From there it's usable in libs: exactly like anything from core/world.
Packaging a library
A package is a directory shaped like packages/world/<name>/, with a package.yaml describing its contents alongside the built output - see Packages for the full schema. How that directory is produced depends on the build system in use.
CMake projects build against $PS2DEV/cmake/ps2dev.cmake as the toolchain file (installed automatically by ps2build update), with CMAKE_INSTALL_PREFIX set to packages/world/<name>. A package.yaml is then written by hand to describe what cmake --install produces. ps2gl and ps2stuff both follow this pattern - their package.yaml files serve as working examples.
Native ps2build projects (a plain ps2.yaml) keep a package.yaml alongside it, naming which build outputs should ship. ps2build install builds into a scratch directory and copies only what package.yaml names into packages/world/<name>. audsrv is an example of this pattern.
Publishing a release: the resulting packages/world/<name>/ directory is zipped and attached to a release. ps2gl's own .forgejo/workflows does this on every tag push, and is a reasonable starting point for CI on a new package.