Analog for Mac it's in my opinion a must-have App. It's incredibly simple and extremely useful. I use it a lot, to modify and apply filters at my photos.
The App has many filters and also some frames (that I personally don't use). There's also the possibility to edit the intensity of the filter you want to apply and of course there're some sharing options. To use the App, you've only to drag and drop the photo (jpeg) on the App and select the filter. Nothing more simple!
Analog for Mac it's available on the Mac App Store for 8.99€ (9.99$). It worths every cents.