I have two knitting apps that I absolutely love and use all the time. Firstly, I have Stitchminder
on both my ipad and my iphone. It is free (more money for yarn! Yay!), simple to use, and customizable enough for my needs. It also has a nice perk of not turning itself off while I am knitting a row. My iphone and ipad have a screensaver mode that kicks in after one minute. This app overrides that so I do not have to put in my password or fingerprint after every row. I am not sure if this app is available for android devices. The price is right to download it, give it a go and see if it works for you. No more row counters lost in the sofa cushions.
I also really love Stashbot
. While this app is not free, it is reasonably priced and worth the money
spent on it. If you are out and about shopping and need some quick math to make sure you buy enough of that dye lot, this app does math for you; sweaters, mittens, socks, shawls, vests - they are all part of this app. I also use it when I am looking at my stash trying to figure out what I can make with the amount of certain yarns that I have. Again, I do not know if this is available for Android devices, but I believe it is available as a booklet at many LYSs
Lastly, one of my favourite iphone/ravelry features is yarnphone.com. I have literally used this all over the continent. If you are travelling and use an iphone, go to Safari, type in yarnphone.com and yarn stores - complete with addresses and directions will appear according to your location. This is an innovation by Casey at Ravelry. It's like a little bit of magic on your iphone.
If you have any amazing knitting apps that you would recommend please put them in the comments.