In the past Welcome Mat, List Builder, Scroll Box and Smart Bar were all separate apps. In 2016 we introduced a new version of List Builder, which combined all 4 of those apps into 1.
If you want to create a brand new List Builder form as either a Welcome Mat, Scroll Box or Smart Bar here's how:
Create a new (or edit an old) List Builder Form
In the Form Type section select either Welcome Mat, Smart Bar or Scroll Box
Set the rest of the form up as you like, and make sure to save with the Make Live button