Cincinnati-based Rabbi Laura Baum’s seder “will be conducted in cyberspace, as her guests – from New York to New Zealand – join in at OurJewishCommunity.org, the online congregation she co-leads. … So far, the guest list is up to about 400 – although she need not worry about any last-minute crashers. ‘It is not as if we will run out of gefilte fish,’ she says.”