Knave is a rules-lite tabletop rpg written by Ben Milton of Questing Beast (and available here). It's OSR compatible, incredibly easy to teach, and even easier to run. Between reading its seven-page rulebook, and rolling characters, you and your players will be dungeoneering and adventuring within minutes. For starters, it's a fairly standard d20+mod roll-over system (as in, roll higher than a target number). If you're experienced with Dungeons & Dragons 5e or Pathfinder, more than anything you're going to be spending more time unlearning things than having to learn anything new.
What I loved
For being so lightweight, it's actually pretty hard to pick a feature that I love the most. Every mechanic and rule within the book has purpose and weight, and is balanced well within the system. Things just make sense. Each of its six traditional ability scores (Strength, Dexterity, Constitution, Intelligence, Wisdom, Charisma) share equal importance so there's never an immediate dump stat. It's classless, but instead of everyone feeling the same, it gives a sense of freedom to let players develop and design their own characters in their own way, relying on what they want to do instead of what abilities they're given to set themselves apart.
That being said, I think the way Knave handles spellcasting is my absolute favorite thing about this system. Technically, anyone can cast spells as they are available in the form of spellbooks. Each spellbook takes a single inventory slot (which are very limited) and allows a single casting per day. Spellbooks also require two hands to use. Mechanically and thematically, this does an amazing job of helping players feel like an actual wizard or fledgling magic-user and reinforces the trope of giving up a weapon, or carrying certain tools and armor in order to wield the power of magic spells.
The spells themselves are widely flavorful, and can be quite powerful in a creative players hands. Knave features 100 level-less spells, but once you read them it's incredibly easy to come up with your own (or borrow the tables from Ben Milton's other game, Maze Rats). My favorite is probably Summon Idol, in which the caster calls forth a carved stone statue the size of a four-post bed from the ground.
Aside from the spellcasting, I think the thing that draws me to this system is just how hackable it is. It's so rules-lite, it's almost a chassis of an rpg, in a good way. If you already have a laundry list of houserules or preferred systems of handling certain rulings (like chases, combat stunts or maneuvers, etc) then more than likely you can port it over and tack it on with no problems. You can hack together a new magic system, alter the current one, or bolt together one from a different system with relative ease. I myself have written a hack called Knacks, or a way for characters to develop different specialties in this post here.
Next Time I Play
Although I love modding and hacking rpgs, whenever I run something the first time, I try to play it as the designer intended it to get an idea for the game itself before making things my own. Next time I run it, I'll definitely be implementing my aforementioned Knack-hack. Also, the players I play with tend to really focus on interpersonal relationships among their characters, so I might try adding some alternate methods of gaining XP through something like bonds and resolving them (similar to Dungeon World's bonds system).
In the weeks reading up on it and preparing our first game, and even just after it, I'm still infatuated with Knave. It's my first foray into the OSR / D&D retroclone space, and my players and I all had a blast with it, already trying to schedule our next play date. For its mechanics, its tables, and its production value it's a steal to be honest. On top of providing a great system of play, there's something about its simplicity and directness that lights those creative lighter fluids on fire for any would-be designer or GM.