I could give you a dog and pony show. Some apps were worthwhile, some not as much. However, I'll point you to the main blog that gave me the most inspiration for what I do... Take a look at financialpanther.com and read carefully what the godfather of side gigs is doing. I use alot of the same apps that financialpanther does. Start with his Side Hustles tab but to get a better idea of what all he's doing, read thru some of the recent monthly blog reports on his side hustle earnings. He's tracked his earnings for quite a while - it's all there.
However, I keep my eyes open and I've gotten a few of my app ideas here on this site and one or two on Craigslist and other places.