jammr Forum

An interesting video about going beyond the 7 chords in a key:
https://www.youtube.com/watch?v=Sn9ZLRbRlgo

If you've looked at chord progressions and wondered how chords outside the 7 diatonic chords can sound good, then this video shows a lot of examples to illustrate the concept more broadly. It doesn't explain them in depth but I found useful information here:
https://en.wikipedia.org/wiki/Secondary_dominant
https://en.wikipedia.org/wiki/Tritone_substitution