Wizards of the Coast provides free PDFs containing the complete core mechanical rules of 5th Edition D&D (combat, exploration, spellcasting, etc.) and a selection of iconic character options, monsters, magic items, etc. drawn from the full game. Though short on variety, the basic rules are playable and accurate to the full game.
Ranked in these QuestionsQuestion Ranking
Pro Easiest tabletop RPG to find someone to play with
As D&D is the largest tabletop RPG franchise and played by most people, it is the easiest tabletop RPG to find players for.
Pro Minimal but versatile rules
5th Edition strikes an impressive balance in keeping the rules simple without limiting the creativity of players.
Pro Bounded Accuracy
Bounded Accuracy is a core design ideal of 5th Edition. In short, it means the numbers don't get too big; this lets weak challenges remain relevant for longer, and strong ones become survivable sooner. In practice, it also places more focus on a character's inherent abilities and less on magical equipment than has been the case in recent editions.
Pro Encourages character immersion
Numerous core aspects of 5th Edition exist solely to encourage thinking in-character, including mechanical rewards for good roleplay and detailed character backgrounds with lasting effects in the game.
Con Lacks variety in various areas
In order to make the character creation fast and relatively simple in-depth customization options have been excluded from the basic ruleset. There's also a limited selection of character options (just 4 classes with a single sub-class), monsters, magic items, etc. The variety is to be found in the full game.