A Review of Quann'Ra-Tioll Moorchlyne's Most Excellent Compilation of all the realms known Ioun stones. A Free Old School Download

This compilation contains more than 600 Ioun stones to brighten up your campaign. This is a great catalog  of Ioun stones for your campaign & so much more . Weighing in at 104 pages this is a nice overview of the stone as a whole, their origins, their use, & those entities that control them. Matthew Hargenrader does a very well thought out job with this OGL material. The layout of the pdf is crisp & to the point. There isn't a metric ton of BS throughout.
The pdf includes an index which is ideal for the DM during play & allows one to deal with necessary treasure on the fly.
I've seen Ioun stone books before during the D20 glut of yesteryear this is much nicer. A better written pdf you will not find. Go Here

Ioun Stones For Space Opera? 

Ioun Stones are the creation of Jack Vance & this pdf places credit where credit is due. There are some old school nods in just the right direction with this. I don't really  associate Ioun stones with Jack  Vance but instead with the Incal books.
The stones were a part of an AD&D game that a friend ran & the stones were being used by the various factions of this universe. I have no idea if it was to save time or simply something caught his eye but there you go.
I think as a weird fantasy or science fantasy  element ioun stones present a host of opportunities.

1. These things make great alien artifact with unpredictable powers & they're not easily associated with science fiction or even science fantasy 
2. They can pop up anywhere or any when. They're perfect for a post apocalyptic universe when you need something alien to convey an invasion or possible source of your Apocalypse
3. The fact that these can be your gate way drug to powers from beyond doesn't need to be said. Elemental or pseudo elemental entities are right on the menu as soon as these appear
4. Nothing says don't screw with the alien or alien princess quite like stones zipping around someone's head or heads. 
5. Given Goblinoid Games various systems or any retroclones this supplement is a fine edition to anyone's library. These would readily work for Terminal space hell even X plorers 
6. Its got the right price tag at free