Grease Pencil Rigs are a free set of basic rigs for Blender 2.8 that are for use with Grease Pencil. They are aimed to ease the drawing of characters by showing construction lines which you can use for reference while drawing.
Johan The Dog is a free quadruped rig for Maya for use in non-commercial projects.
Grey Matter Gary is a free Maya rig from Squiggly Rigs
The AZRI Rig is a simple animation rig for Maya 2018 and above, representative of video game projects aimed at retaining a high frame rate when working even on lower-end machines. Featured in the book, ‘Game Anim’
Red Dragon Rig is a free Maya rig made by junior rigger, Elise Mathez
Fantasy Crocodile Rig is a free Maya rig that has a super appealing design.
Rocket Girl Rig is a free Maya rig from the VMComix animation blog.
Jasmine Rig is a free rig for Maya that has a load of great features!
Tri Vital has created a collection of awesome Maya rigs and put them on gumroad for free!