Many great comments. It is most commendable to want to maximise one's own positive impact on the world, but figuring out how exactly to do that is incredibly complicated - as the variety of opinions here demonstrates. In truth, many (or most) of the people or organisations that try to help out make virtually no difference, and sometimes make things worse. And to make things trickier, the best way to make the world a better place is incredibly personal, and depends on your skills, motivation, life stage, connections, preferences, etc.
Yet, that doesn't mean that it's impossible.
I've been there: now I am working on launching my own tech start-up (how unoriginal), but prior to this I worked in Africa and Latin America.for 4 years, designing projects to create sustainable jobs and to increase long-term income of small farmers. And I've seen so much waste, and incompetence, and worse... and a few pearls in unexpected places.
In short, it's not something one can improvise, creating something genuinely good is probably the most difficult thing in the planet, definitely not a little side project.
So, the best I can suggest is: read a lot, be suspicious of simple blanket solutions, develop your own opinions, and, most importantly, find 1-2 people with experience you can trust (not necessarily techies!), and learn from them.