LibHunt - LibHunt tracks mentions of software libraries on relevant social networks. Based on that data, you can find the most popular projects and their alternatives.
Slack Overflow - A programmer's best friend, now in Slack.
AlternativeTo - AlternativeTo lets you find apps and software for Windows, Mac, Linux, iPhone, iPad, Android, Android Tablets, Web Apps, Online, Windows Tablets and more by recommending alternatives to apps you already know.
GitCommands - An interactive reference tool for Git commands
JSter - JSter is a community-driven catalog of the most useful javascript libraries.
GitHub + Slack Integration - Full visibility into your GitHub projects right inside Slack