Sanjit Biswas, 25

Sanjit Biswas worked on a system for connecting local residents to the Internet wirelessly. In 2006, a nonprofit group asked if the technology could help provide Internet service to the poor. Intrigued, Biswas took a leave of absence to cofound Meraki Networks in Mountain View, CA, and create wireless mesh networks that would link people to the Internet cheaply.

In most mesh networks, all the nodes that receive a particular data packet forward it on; but in Biswas's version, the nodes "talk" to each other and decide, on the basis of the packet's destination and their own signal strengths, which one of them should forward it. The protocol also takes into account changing network conditions, as users sign on or off, or, say, a passing truck blocks a node's radio signal. Biswas's protocol, combined with commonly available hardware components, allows Meraki to produce Wi-Fi routers that cost as little as $50. (The routers Biswas used at MIT initially cost $1,500.)

Here's how a Meraki network works: a user plugs a router into a broadband Internet connection; that person's neighbors stick routers to their windows, and a mesh network of up to hundreds of people forms automatically. Users can give away or sell Internet access to their neighbors. There are already Meraki-based networks in 25 countries, from Slovakia to Venezuela, serving more than 15,000 users.

--Neil Savage