Boston and Cambridge go to great lengths to attract the tech sector’s big guns like Facebook and Google, but it’s the little guys that can have the most impact. That’s the philosophy behind MassChallenge, the world’s largest start-up accelerator program. Each year, it awards more than a million dollars in grants to up-and-coming companies.

On Wednesday, MassChallenge announced at WGBH the 128 finalists, who run the gamut from bio-med companies to social welfare initiatives. 

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