When Japan's Ibuki climate satellite orbited January 22, it had hitchhikers: no fewer than seven microspacecraft with scientific and demonstration missions:
SDS-1 (Small Demonstration Satellite 1)
SOHLA-1 (Space Oriented Higashiosaka Leading Association)
PRISM (Pico-satellite for Remote-sensing and Innovative Space Missions)
KKS-1 (Kouku-Kosen-Satellite 1)
SpriteSAT is one of my favorite examples of what you can do with smallsats, thanks to its fascinating mission. This a sub-50kg spacecraft was built by university students and faculty to observe a powerful phenomenon we didn't know existed until a few years ago (electrical discharges called "sprites" in the upper atmosphere).
STARS-1 is a tether experiment, with a "mother daughter" pair of spacecraft. Tethers are potentially useful for control, orbit-raising, and power-generating purposes, but tether experiments seem jinxed, with several encountering glitches or (in one case) launch failure. Here's hoping for better luck.