Stanford Doggo: https://nathankau.com/Research https://github.com/Nate711/StanfordDoggoProject

Here is an open-source, 3D-printable quadruped with (almost) direct-drive actuation:

https://open-dynamic-robot-initiative.github.io

Paper: https://arxiv.org/pdf/1910.00093.pdf

Videos: https://www.youtube.com/watch?v=MkXU-5Oupg4

Here are two:

MIT Cheetah: https://biomimetics.mit.edu/

Unitree/laikago: http://www.unitree.cc/