> Most Google apps supports a way to have multiple Google accounts active, typically by adding /u/[numeric index of a specific Google account]

FWIW: instead of manually entering the numeric index, you can enter the full email address instead. so you can enter /u/[email protected] or /u/[email protected]. This is handy because the numeric index depends on the order in which you logged into (added) the accounts and I don't want to have to remember that!