I've been using Kodi (formerly XBMC) since "Frodo", now "Krypton" (version 17), waiting for "Leia" (v.18) to become stable...
It's open source. (GNU GPL version 3)
HUGE selection of addons including YouTube, Food Network, and so on
ANYONE can write an addon! The addon language is Python. If you can write Python code, you're in.
Cross platform! Linux (Ubuntu, Debian, Fedora...), Windows, Mac, Android (no iPhones)... even Raspberry Pi... and Apple TV, also for Xbox One through the Microsoft Store
extensive documentation at https://kodi.wiki and user forums
Can be a tad difficult to set up.
YouTube addon search function can error out (but can be solved by creating a free Google API key)
Oh... the website is kodi.tv not xbmc.org anymore because Microsoft sued the developers for unauthorized use of Xbox (Kodi/XBMC was originally for jailbroken Xboxes [the original not the Xbox 360 or Xbox One])