This article mentions the deployment of a couple of "subsatellites" into lunar orbit from the Apollo 15 and 16 spacecraft. I had never previously heard of any such action being taken. Where were these subsatellites stowed aboard the Apollo spacecraft, and how were they released from it? Did they have their own thrust capability for deployment?
They were deployed from the Scientific Instrument Module (SIM) bay in the Service Module. There's a long write-up here. The launcher was spring-loaded.
The SIM bay was a volume in the Service Module which was loaded with scientific instruments. The SIM bay cover was jettisoned around 75 hours into the mission according to The Apollo Scientific Instrument Module (SIM) Cameras website.
Besides the subsatellites, one of the major scientific payloads consisted of film cameras. The CM pilot did an EVA to retrieve the film.
Artist's rendition from wikipedia including the satellite (I just noticed this picture was in the article you started with, so I outlined the SIM bay):
And here's a real picture of the SIM bay:
There's a long history of spring-loaded small subsatellite launches throughout the US human spaceflight program. The last picture ever taken of a Shuttle in space was taken from just such a subsatellite: