These are called "AAC devices" (alternative and augmentative communication). They come in a variety of forms and are designed for people who cannot communicate verbally at all, usually because of things like cerebral palsy, severe autism, ALS, etc. Some have a keyboard, others have picture banks where you select based on images. Some will have a computer voice said what you type (a la Stephen Hawking), others will just display the words for your listener to read. Dedicated AAC devices that are designed to do nothing but AAC are usually VERY expensive-- thousands of dollars. Ironically, ones that are based on a preexisting piece of general technology (iPad + AAC app) are much cheaper (though still $$ if you factor cost of the iPad and app; the app cost can be a few hundred $). Honestly, if you have normal IQ and no fine motor impairments, you likely are best off with a regular text-to-speech app that you can use on a phone/tablet and that only costs a few dollars. A lot of AAC devices are designed for people with serious and complex disabilities, and the form factor is slow and clunky to account for things like motor impairments. But, if you want to learn more, google "AAC device" and you should be on your way!