A website popped up earlier this year called See Muscat, it's been building steam and they guys behind it have launched an app for their website on both Android and Apple. I wrote about the website briefly earlier this year, and they've gone from strength to strength.
Check out their website, and if you like what you see, go get the app, it's free, for your phone - to get it on your phone just click on this link, and it'll send you to the right place (Android or Apple only).
My only issue with the app is that it's currently not searchable - you can click different areas to "search" for things, but there's no search prompt.... but I'm told this is being developed and will be rolled out in a future update.
It's really a pretty handy app, I'd imagine especially for those people visiting Muscat.