This small add-on module to Simplenews provides a new block which lets users subscribe or unsubscribe to all of your newsletters in a single operation. Simplenews itself provides one block for each newsletter, which is good in some cases, but can make your site look cluttered if you have many newsletters. This module takes the combined form that Simplenews already provides at
newsletter/subscriptions and displays it in a block.
The goal is to eventually have this functionality included in Simplenews proper.