Connect freelancers to companies, money earned goes to charity
A job-board & project-management tool (like oDesk) which connects web-enabled freelancers (writers, coders, designers, etc) with companies. The project management bit is for ticketing and time-tracking, the hourly earnings are escrowed to charities of the freelancer's choice.
Think Samasource minus outsourcing. If a company wants tech skills from local talent rather than via outsourcing (which is often the case), they would use this tool. Instead of hiring paid-for talent, they find freelancer volunteers & still gain feel-good & PR props :) The freelancer would pick up this work as do-gooder programming (the money earned goes to his chosen charity) and can write off the earnings as tax deductible.
Note: This isn't a "build my nonprofit website" job board, these would be for-profits because (1) there would be real money (competitive salary, which the freelancer donates), (2) more available work than the former, (3) there are plenty of job boards for the former.