Maybe it's a random itch.io find; maybe it's a minor title from a long forgotten console; maybe it's a dev project your friend asked you to play test. Whatever it is, you think it's neat, and you never see it mentioned anywhere.

Tell us about the game -- what is it? Why is it noteworthy? Do you think it deserves more recognition than it's gotten? Why do you think it's as hidden away as it is?

For people new to tabletop RPGs, this is the equivalent of a DLC expansion. It's new content, new rules, new classes, and so forth to augment your 5e game.

Notable contents include:

Racial Traits

1. Racial stat bonuses can be moved around at will (i.e you can change a Half Elf's +2 Charisma to a +2 Strength)

2. Races with negative stat bonuses no longer have negative stat bonuses

3. A new "custom lineage" race exists, which allows to pick any race, and replace their features with a +2 to any stat of your choice, a feat, and darkvision.

Class Variants

These modify class features. Unfortunately, many of them are somewhat controversial in the community because people do not believe that they fixed many of the classes that are considered to have poor design, notably rangers and sorcerers.

For the spellcasters, spell versatility (a feature which allows you to change spells you know on a long rest) was not implemented, disappointing many

New Subclasses

A few subclasses from other books are reprinted so you don't have to buy them (example: Eloquence Bard, from Mythical Odyssey of Theros), and a few are new, like Order Cleric, Wildfire Druid, and so forth.

In particular, the Clockwork Soul Sorcerer is one piece of good news for Sorcerer players.

Live feed in French - in the last 10 minutes nobody really knew what was happening according to my relatively bad french.

Montreal Gazette - will be updated

The trend on twitter - for some up-to-the-minute information and slight hysteria

An article via Gamasutra - this just happened to be the first one I read, will also likely get updated.