Gramar is important to me, so when I realize that I've mis-used something, it makes me a little crazy. I know that many people don't find it to be of utmost importance that grammar be used properly, but for me, it feels dangerously possible that my point will not be made as I intend it to be if I cannot utilize the appropriate words. I'm also practicing with run-on sentences. Can you tell? :)
I find that www.grammarbook.com is super easy to use, and their search features are great. Also, the author passed away recently. Her name was Jane Straus and now you know as much as I do about that.
I've never though to look for an App, since I'm usually sitting in front of my computer when I'm having grammar quandaries.