chordAlchemy - Cool software for chord, scale and reverse-lookup for Guitar, Banjo, Mandolin, Bass and Ukulele! Indispensible for understanding how chords are built, what keys and scales are, and what their component notes are. Warmly recommended.
Have a stroll over and check it out. You might even “Like” it while you’re there... ;)
John Kean’s indispensable guide that is extremely well written and easy to understand. But for those with an academic musical background, you’ll know this stuff, anyway.
If you have to wash your hands after playing your guitar, then it’s time...!
An on-line tuning tool for a range of stringed instruments. Choose your instrument and get tuned... Easy!
The cover songs database. It gives information on the dates of original versions of songs, as well as the dates on significant cover versions.