It's something you can apply in your own life. If you think someone did something nice or good, just tell them. Don't make a big thing out of it; but just make sure to let them know when you get the opportunity. Most people will really appreciate that and might get motivated by that. This sounds simple but a lot of people don't do this or are a bit shy about it. Of course the value of your compliments decreases with the frequency you give them so it helps being a bit genuine about it and to not overdue it. Something simple as using the star button in github, adding a little thumbs up to an issue in an issue tracker, or upvoting a comment on HN is what keeps the good stuff going.

A lot of stuff that people do for free is rather thankless work except for the occasional appreciation. I've been maintaining some only modestly popular OSS projects on Github. They won't change the world and I mostly do it because it serves my own needs. But getting the occasional outreach from people that used some of my code is always a highlight in my day.