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.

Slack Overflow - A programmer's best friend, now in Slack.

Ruby Toolbox - Explore and compare open source Ruby libraries

GitCommands - An interactive reference tool for Git commands

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.

GitHub + Slack Integration - Full visibility into your GitHub projects right inside Slack