Lecture notes

The following is a list of exceptionally well-written lecture notes on certain topics in geometric group theory:

Median Algebras

Brian Bowditch

Algebraic properties of groups acting on Median graphs

Anthony Genevois 

Lecture notes on GGT  

Alex Sisto

CAT(0) cube complexes, median graphs, and cubulating groups 

Mark Hagen

What is a hierarchichally hyperbolic space? 

Alex Sisto

https://flab.perso.math.cnrs.fr/preprints/whatis.pdf

What is a cross ratio?

François Labourie