I wish there was a device to keep guitars in tune! The reason Hendrix needed to tune so often was he used the “whammy bar” so often. Aggressive use pulls the guitar out of tune. In the 1980s thay came out with locking systems actually clamp the guitar strings so they stay in tune during whammy bar use. But they are a pain to change strings. The 80’s shredders liked them but not many guitar players use them anymore. Plus, most guitars are better made now so they hold their tuning longer. I can usually play through a whole 2 or 3 hour gig without tuning my Telecaster.
Yes, looper pedals are fairly common now. You can record a section of chords while singing and then loop it to solo over it live. Which is different than using pre-recording music because you did it all live in front of an audience. They are very popular with solo acts. There are also octave pedals that will add a note an octave lower or higher. There are even harmonizers that will add harmony notes. Singer sometimes use them live if their bandmates can’t sing. LOL!