MindSumo helps employers host skill-based projects for students, who can then compete for cash prizes and entry-level jobs/internships. Over 500 employers use MindSumo, and they have awarded over $100,000 in cash prizes to date.

See the following three challenges:

Groupon Challenge: What is the best way to leverage HTML5 in our mobile apps?
Zappos Challenge: Write an application to help customers find the right price.
Addepar Challenge: Can your dev tool boost engineering productivity?