Just launched today as an Indiegogo campaign (and over a quarter of the way to the goal as I am writing this) is an interesting product idea called DIMPLE from dimple.io. Dimple is basically a sticker with 4 buttons that can be added to many Android 4.0+ devices that support Near Field Communication (NFC) and the Dimple app. It requires no batteries because it uses energy that is radiated by the NFC reader.
This prototype product is not one made specifically for people with disabilities—obviously from the response on Indiegogo, many people are interested in having customizable, programmable tactile buttons on their smartphones and tablets.
Dimple has potential accessibility uses. Such buttons would be useful for people who cannot see, because the buttons can be tactilely discerned and located. These users could associate some of their most commonly used functionality with the buttons and access them directly, instead of having to navigate through menus with the TalkBalk screen reader.
I do not know the exact capabilities of DIMPLE, NFC, or Android TalkBalk, but it would be very useful if the Dimple buttons could be used to access the TalkBalk screen reader or to generate virtual keyboard keystrokes. If capable, it would be very useful to have dedicated buttons to navigate through applications and make selections. This would be less fatiguing than making many swiping gestures to navigate.