Ask HN: What's your startup or product?

I thought it would be interesting to hear about the software projects people are developing. It's amazing and inspiring to see what problems people are solving through software. So, what product or app have you developed or are you working on? It can be anything from a full-blown startup to a small side-project to a quick hack.

Please keep in relatively short.

(Old version of this question here: https://news.ycombinator.com/item?id=4378909 Copied some text from it because I'm optimizing for throughput:)