I did most of the code alone. @cass helped me bigtime with the logo and wants to assists with design/layout aswell. Hoping for @svk to assist on the trading page eventually.
Piston itself build on top of 2 more libraries that I wrote as well:

• python-steem (which itself build on)
• python-graphenelib (mostly known from the BitShares community, graphene is the underlying technology)

Been working on python-graphenelib for years now :)