The best alternatives to Fretboard Forever are ChordIQ, Fretboard Learning, and Fretboard Fly. If these 3 options don't work for you, we've listed a few more alternatives below.
Mastering the guitar fretboard is hard. Memorizing notes, intervals, triads, chords etc. is really important to progress but also really boring and hard to stay on top consistently. Fretboard Fly turns it into a fun game, so you become a better player.
Fretboarder is a web app to visualize the layout of scales and arpeggios on a variety of fretboards, from ukulele to 11-string guitar. It can overlap multiple sequences, display specific positions, highlight intervals, and more!
πΈππ€ A simple web app that makes it easy to learn the notes and practices scales on the guitar. Try out different tunings and highlight/play the notes of specific scales on the fretboard.