Pre-Launch Widget Templates - 100+ widgets for your pre-launch campaigns
Bootstrap 4 Cheat Sheet - An interactive Bootstrap 4 cheat sheet
GoodUI Fastforward - Lift your conversion rate with repeatedly AB tested patterns
Bootstrap Zero - Open-source, free Bootstrap templates collection.
CloudApp - CloudApp allows you to share images, links, music, videos and files. Here is how it works: choose a file, drag it to the menubar and let us take care of the rest.
HackerThemes - Bootstrap 4 themes and tools for web developers