FaceApp was launched a few years ago, but it's going viral again because of its new features with filters that make you look younger or older.
And of course, many people are having fun with it, including celebrities.
Rapper Drake encouraged fans to caption his old photo.
Houston Texans star J.J. Watt shared aged version of himself on Instagram with the caption "Mandatory daily naps for the whole nation."
Here's Gordon Ramsay, writing that this is what he would look like doing season 50 of "Master Chef."
Some people joked about it and took it to the extreme. Screenwriter Gary Graham tweeted a photo of a mummy, saying that's what he would look like in 60 years.
And others decided to use the app to see how their favorite celebrities would look.
MORE FACEAPP PHOTOS FROM CELEBRITIES AND ATHLETES
There are privacy concerns about the app. A team from Saint Petersburg, Russia, reportedly admits they "may share user content and your information with businesses."