We're another example of a non-profit tech startup: https://www.engageSPARK.com . We're a slightly different model in that while we focus on selling our engagement platform (think "Twilio for non-techies") to non-profit customers globally, we have lots of commercial customers who use our platform for marketing purposes. Having a diversified revenue stream helps greatly with sustainability.
Check out Fast Forward, an accelerator focusing exclusively on non-profit tech startups: https://www.ffwd.org . Y Combinator now also has a track for non-profits - https://www.ycombinator.com/nonprofits/ and for example funded https://watsi.org/ .
Feel free to ask questions. I volunteered at Grameen Foundation and have been exploring this space for a while.