I am using little Japanese tractor (Kubota) built in 80s on my farm. There is thriving industry importing those directly from Japan. They are very simple, there is basically no electronics, everything could be repaired by hammer and will last lifetime. Only downside is that even 25 years old tractor is still more expensive then my car, but it is still worth it.

If somebody want to improve the world and help poorest they should just invent ways to produce those inexpensively and sell them in poor areas. Productivity will skyrocket.