Snapseed is a simple and effective application for both iOS and OSX for conferring special effects on pictures. I mostly use it to add grunge in those snaps which merit the treatment.
Now the two major issues I had with the OS X version of the application have been fixed by Nik Software. First, you can export to Snapseed directly from Lightroom and second the application will now accept TIFF files rather than just JPGs. I have tested both and can confirm the revised version does both perfectly, and when you save the file it’s stacked with the original in Lightroom.
Here’s a snap processed in Snapseed with grunge, vintage effect and frame added:
On Broadway, SF. D700, 105mm f/2.5 Nikkor-P at f/11.