This app was mentioned in 10 comments, with an average of 1.70 upvotes
I've downloaded a app on Google play store called cookpad, https://play.google.com/store/apps/details?id=com.mufumbo.android.recipe.search just search low carb, or high protein. My wife is doing the no/low carb thing, I'm also diabetic so it benefits me also. Good luck.
I like All the Cooks. The app itself is well designed, and it's easy to save and organize recipes. It's also got Android Wear support which is very nice if you have a Android Wear smartwatch.
Its a community based cookbook - all the recipes are submitted by users. A few of the recipes are just bad, but other recipes are amazing and stuff you wouldn't find in a regular cookbook (cookie dough pancakes, and pizza filled veggie rolls to name a few I enjoyed at college).
I use the Cookpad app for anything that I have to record.
Duolingo is fun enough for language, and they have web games too.
Allthecooks is great for recipes.
Guitar Tuna is good for learning guitar strings.
Money Lover is good for keeping track of finances.
(These are just ones I had)