That app is GifLab, and it claims to be the “easiest way to create GIFs on your iOS device”.
Created by Museworks, GifLab lets you snap new footage or use existing video and quickly turn it into a shareable GIF. You can also apply a range of filters, impose text and place emoji over your creations. The apps super easy user interface also lets you tweak both the speed and quality of the resulting file before sending it on to your friends.
When it comes to sharing, the app lets you send it via Messages, save your creation to your camera roll and even upload it online. Other sharing options can also be surfaced via the iOS share sheet.
The universal app is free to download and use, but additional filters, fonts and features can be bought via various in-app purchases.