I'm surprised no one here has yet mentioned https://www.codeshelver.com

>Codeshelver lets you clean up your GitHub watchlist by storing repositories you would like to remember on your shelf. You can tag any repository and search for it later on - until then it won't spam your dashboard timeline.

Codeshelver helps you find that one project that you had seen ages ago, which you did not want to follow (watch), but perhaps use somewhere.