Aside from Facebook and Pinterest, the app that I use the most is MyFitnessPal. I can't remember if this app was already mentioned in a previous Thing (it probably was). If not, it's a great app for helping track exercise and food intake. What I like about it is that it's more complex than just tracking calories and fat but also tracks protein, carbs, vitamins, and minerals.
There are two new apps I recently discovered but haven't spent much time using yet. They are Charity Miles (http://www.charitymiles.org/) and Play to Cure - "Genes in Space" (http://www.cancerresearchuk.org/support-us/play-to-cure-genes-in-space).
With Charity Miles you can track a workout and earn money for a charity of your choice. Per the website: "It's as easy as this: get moving. Bikers earn 10¢ a mile and walkers and runners earn 25¢ a mile, up to our initial $1,000,000 sponsorship pool." I haven't tried it out yet, but it certainly sounds like a great idea.
The other app is a game and the website claims, "By playing Genes in Space you'll be analysing significant amounts of genetic data which would have taken scientists hours to do. This data can then be used to develop new life saving treatments." Again, I haven't tried it yet but what a cool idea!
And this isn't necessarily an app but I just found out about Amazon Smile! It's regular Amazon except that they will donate 0.5% of your eligible purchase to a charity of your choice. Nice!