While working at Coull, I've worked on the backend systems which our clients integrate with. I've helped transition from PHP to Go, and reaching a scale of over 4 million requests/minute.
When working at Loccit, I had to do lots of jobs being at a small startup. So my most impressive accomplishment is at some point managing a team of developers, while at the same time being the main developer for our internal API (PHP/MySQL/Redis, being the main developer of our native Android app, doing part of the website backend (PHP/CodeIgniter/MySQL/Redis/beanstalkd) and even helping out with the frontend of the website (HTML/CSS/Compass-SASS/jQuery/underscore.js).
While working at Loccit, we started using http://sprint.ly for managing the team. Being a new product that had an API but no mobile apps, I created in my spare time the first Android Sprint.ly client (http://bit.ly/AndroidSprinter).