There currently is at least one more example of this. The base concept is called a user-space object manager. The idea is that an application may have objects that exist outside the OS model that it wants to mediate access over. For instance an application may store its information in one file which the OS can label however that file is composed of a bunch of application specific objects. I'm sure KaiGai has a much better description than I can hope to give in his documentation.
In addition to SE-Postgres work has been done in the X server to provide a framework similar to the LSM framework called XACE (X Access Control Extensions). Just like the LSM framework you can create modules for XACE and one for SELinux has been developed. So the X server is acting as the enforcement mechanism and it queries the kernel security server to ask about access decisions just like SE-Postgres does.