When it comes to psionics, I'm usually a bit of a skeptic when it comes to people's implementation of it in 5th edition - I firmly believe that psionics should not be some entirely different, mechanically esoteric subsystem that clashes with how magic is already mechanically presented within the existing game rules.
From the same person who brought you Adventurer's Almanac however comes the Psion's Primer, which presents a version of psionics that is both novel yet within the established parameters for how such a system should work in D&D 5e, not merely as a generic lore-agnostic ruleset , but in an Eberron-first way (though a number of sections talk about how to use this book elsewhere) - while Eberron might not be the first setting one might think of when they think about psionics, but there is a significant chunk of it (a whole continent!) that is very difficult to properly represent without some form thereof, and the Primer is an excellent resource for that very purpose.
The basic workings of psionics build upon the existing rules for spellcasting, but rearrange and tweak things just slightly enough to feel different without being oddly complicated, but the book contains far more than just simply how psionics operate.
Firstly, it provides two completely new classes, who manage to be meaningfully different from each another, beyond simply being "psionic fullcasters" - the Psion who's of thought and logic in the vein of a wizard, and the Empath who's of emotion and belief (like a cleric). This is a pretty clever distinction to what in another similar book might have been rolled under a singular class - comparable to there being simply one "Mage" class for regular magic, which we know isn't how D&D handles it.
You also get three new subclasses for the existing classes (the Lurk rogue, the Soulknife monk, and the Adamant fighter), allowing them to tap into the new options presented in the book.
Beyond that, you get a number of new racial options - fans of the 3.5 XPH (and even 2nd edition DS) psionics will immediately recognize the likes of thri-kreen, blue goblins, elans and the gith, while 3.5 Eberron fans will appreciate the return of properly-psionic kalashtar, Akiak duergar, the psiforged, and some technically new but perfectly-fitting daelkyr madbloods and dreamscarred goliaths.
Next up we have some new psionic feats, equipment and magic items - a nice selection of options that play well with the rest of the book's contents. Some random examples of the items include crysteel weapons, a new category of magic items in the form of tattoos, and new psionc ioun stone options.
Following that, we get to what's probably the meatiest part of the book - the psionic powers themselves. Split between talents (which function like cantrips) and augments (which further empower them), you get a little over 50 pages' worth of powers - enough to execute a vast array of psionic character ideas, but not so many that your mind starts taking psychic damage. The preceeding chapters all hook into this one in some form or another, meaning it is not simply a 56-page appendix for the Psion class alone.
Last but not least, we get to the more DM-oriented chapter featuring stat blocks for a number of psionic NPCs and monsters - from characters that utilize the new psionic class and subclass options, to properly-psionic mind flayers and daelkyr, to cerebrelith demons, the gith and more.
Overall, this is not just a way of handling psionic characters in 5th edition, but a complete psionically-themed package for Eberron and other settings - it touches on every major facet of the 5e ruleset, and is just barely shy of a full-length professional 3.5 or 4e-era supplement, and the overall quality of writing and design on display is on par with some of the best that Wizards of the Coast might have put out back then - if not better, depending on how you feel about the recent attempts at bringing psionics to 5e through the Unearthed Arcana playtest articles.
And you can get it for only ten dollars!
Final verdict? If you want to play a psionic-oriented campaign, or give your players some psionic options in an ongoing campaign, make sure to grab this book - especially if you play in Eberron, where these will slot in with no hassle.