My first and usually last stop when I need sheetmusic or methods.
https://www.penders.com
Bach’s Fugues Brilliantly Described using Animation and Metaphors
https://jan.ucc.nau.edu/~tas3/wtc.html
Excellent resource with online guitar tuner and metronome.
https://8notes.com/
From tabs to instruments, hard to surpass. https://www.harmonycentral.com
Lots of old fashioned methods. https://www.bostonmusiccompany.com/