How to Restrain?

[Ravenlute]

What are the different ways you can Restrain somebody?

I've seen getting a Crit on a grapple check.
Binding with rope or manacles.

Are there any others?

[Tarpeius]

There are a handful of spells: Transmute Rock and Mud, Upheaval, Wall of Flesh. Many creatures have abilities that restrain. Getting buried by snow or other huge quantities of stuff also does the job.