Below are a few of my favorite recommendations for making computers and iPads switch-accessible:
1. Switch Interface
A switch interface students to use switches with computers, for the purpose of activating cause & effect software, or advancing slides on a PowerPoint presentation with pictures/sound/other stimuli.
2. Bluetooth Switch
A bluetooth switch connects to iOs devices via Bluetooth, allowing students to use some iPad applications via switch activation.
3. SEN Switcher
SEN Switcher is a free cause & effect program online, with multiple levels and customization options.
4. Switch-accessible iPad Apps
Click here for a list maintained by Jane Farrall of which iPad apps are indeed switch accessible: