Some four million people in India suffer from cerebral palsy and other disabilities that make it difficult or impossible for them to speak. Giving them a voice is the job of Ajit Narayanan's low-cost tablet-based system, Avaz. Even someone with only limited movement control can use Avaz to construct phrases that are spoken out loud by an artificial voice.

Speech synthesizers have long been used in the West (perhaps most famously by Stephen Hawking), but they are prohibitively expensive to all but the richest in India. Narayanan's Invention Labs, based in Chennai, designed Avaz to be not only cheap but also capable of supporting multiple languages. "The average young person in India speaks and uses three different languages every day," Narayanan points out. By working directly with Asian hardware manufacturers, he has been able to bring the cost of an Avaz down to around $800, compared with $5,000 to $10,000 for a single-­language device in the United States.

Just over 100 of the devices have been sold so far, mainly to specialist schools, and they are in use by around 500 children. "I've seen parents weep when Avaz allows them to talk with their [child] for the first time," says Narayanan. He is currently working with the Indian Institute of Science, Bangalore, to improve the quality of the speech synthesis, and he also plans to use mobile app stores to distribute a version of his software with about 90 percent of the full Avaz system's functionality. —Tom Simonite