It's called Thankful For, and it is pretty awesome. It simply poses the question "What are you thankful for today?" and lets users add to their own personal gratitude journal, as well as a wall of public thanks, which shares what "The world is thankful for..." Plus there are some inspirational quotes. You can post on the website too, for those without a smart device.
I have a new tradition of starting my morning by adding one thing I am thankful for to my journal. Some things that I have added include:
"watching the cats run out onto the screen porch to hear the birds first thing in the morning"
"morning drives along the lake"
" supportive friends and colleagues"
"A kind and patient boyfriend"
What are you thankful for?