I don't think tech people should build tech things in hackathons to "help" charities/communities and the like.
If you build something, it should be built, and supported.
Something built in that way lacks support and often care and attention. It's a prototype.
However I've seen too many good ideas get built, and then simply thrown at a community.
The techies think they're "doing good" and the community thinks they're great for about 5 mins
Then, often, the techies are nowhere to be found.
Not always though, and there are always exceptions.
The point is that tech people shouldn't try to do good by "building tech"
Tech people should be doing good by not doing tech.
This kind of thinking often misses the "why not just buy him a cup of coffee?" and the "just squeeze it with your hands?" type of thinking.
Doing good isn't about doing tech.
A lot of the time, tech facilitates people to do good.
When you think about your next side project or hackathon and want to "do good" why not consider that instead of building something cool?
They don't require updates, they give people information and they facilitate and inform people to take action.
Change the world. And if necessary, use tech.