Our dev team at Codementor (https://www.codementor.io) made this side project over Christmas analyzing the most popular & fastest growing product categories of Product Hunt in 2015. We're really curious about what have become popular and if there are any interesting trends in 2015.
Video & photo apps have remained popular in 2015, while Apple Watch & Slack apps have arrived at the scene with the biggest growth.
Please check it out - would love your feedback!