Google Open Source - All of Googles open source projects under a single umbrella
Likewise - Get recommendations you love, from people you know.
Opensource Builders - Find open-source alternatives to commercial apps
Alternative Hunt - Learn about great alternative products as you browse the web
LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
Alternative To by SaaSHub - Find the alternative to every product with a single click