Built a React App
Designed a product
Built a Java service
Broke through government bureaucracy
Integrated with governmental systems
Helped build Tuleva, the first non-bank pension fund in Estonia.

Estonia's classic pension funds were the worst-performing pension funds in Europe. A few folks crowdfunded the initial 3 million required to start a new one, then we worked through quite a few fun hurdles to ship the initial version of Tuleva, which is based on Bogle's classic thesis of low value market tracking. This entirely changed the market of pension funds in Estonia, where banks have finally started offering worthy competition based on index funds. Tuleva is still the best in town, though.

I still contribute a few times a year.