I used to play guitar well but due to an accident I now cannot play it due to my left hand not being able to fret it correctly. Is there another stringed instrument that would be easier to fret with the left hand? Someone mentioned the banjo?
Difficult to give a suggestion without knowing in detail exactly what your left hand can and cannot do, but I cannot help thinking about Django Reinhardt, and what he was able to do even after losing two fingers in a fire...if you haven't read his story yet, you might want to do so, maybe starting from his wikipedia page and some youtube videos:
While there are quite a few recordings of his, videos that show him playing are very rare, so, just to give an idea of what it may have looked like when he was playing full out, here's a modern rendition of one of his most popular tunes:
What comes to mind for me right now is lap steel or dobro. Both are instruments that have much in common with regular 6 string guitar but don't require fretting in the traditional manner, instead open tuning makes possible chords using a bar, and you can also play scales and modes, but will need to learn new scale note placement because of the open tuning. I may be assuming to much, but your mentioning learning to play banjo leads me to believe the music you are interested in playing may be bluegrass and both instruments fit nicely in that category. Perhaps further detail in your original post might inspire other ideas.
I don't really find banjo or bass guitar easier to fret than guitar. But that is just my opinion.
What I would attempt first in your case, is to put on lighter strings on your guitar. If that isn't enough, you could try to tune it down a couple of half steps, since it will make the strings less tense. This is of course only a reasonable solution if you are playing alone. You have to readjust/rearrange the music you are playing when playing with others, which is not always something you wish to do.
A more extreme solution is of course to switch over to left handed guitar. If your left hand is up to play what your right hand normally did.