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Steam Families is here
(store.steampowered.com)
Steam is a video game digital distribution service by Valve.
Steam News | Steam Beta Client news
Useful tools:
SteamDB
SteamCharts
Issue tracker for Linux version of Steam
My guess is this, which is way at the bottom of the support FAQ page (which can be found at the bottom of the posted FAQ section):
"I cannot join a Steam Family"
If you cannot join a Steam Family, it is likely for one of three reasons: