Grog's knots is always a good one and the Orvis app is good, but they both cost money. I got a free knot app simply called "fishing knots"...pic of a hook on a green background, that's okay. Didn't find much else worth downloading.
Fishhound is great and its free. I don't have any paid apps so can't speak on those but fish hound has a index of flies based on what you are fishing for plus you can get reports on water but those are not the best as there are not enough ppl posting them for the bodys of water I fish.
I am using it on android 4.1.2 and it has worked well. No crashes or hangs. I have had issues with it pulling info from a few specific tide stations, but other then that it has been great.
Edit: By issues, I mean it throws an error message when it can not contact a tide station. I have had this last for a day at the longest, I think its more on connectivity to the station and not the app.
Go to your settings and clear your cache. That usually fixes it for me. The admin error is just a message stating that WFF isn't compatible and you are the forum administrator (you aren't) that it should be updated to remain compatible. However I remember someone saying that eventually tapatalk will no longer work.