It is called
Create A Pattern Tool
It can be downloaded from here:
What they say about it:
Create and share your own original patterns with The Sims™ 3 Create a Pattern Tool. Whether you’ve been hankering for a new plaid for your Sims’ PJs or an exquisite flourish of tiles for their floors, everything you want to create is now within your grasp! Design a pattern quickly using dozens of images available in the Sticker Library or layer and modify your own images to create even more unique patterns. Expand your creativity and share your creations online through The Sims 3 Exchange.
As the official pattern tool for The Sims 3, The Sims 3 Create a Pattern Tool makes it easy for you to make your own patterns and ensures that your designs and game will remain intact.
Apply your newly created patterns to your Sims’ furniture, clothing, floors, walls, and more!
This powerful yet easy-to-use tool is perfect for all types of users ranging from beginners to advanced designers.
Preview your patterns in 3D with the click of a button, then export directly to your game.
Show off your creations to Sims fans around the world through The Sims 3 Exchange.