Osamu Higuchi at Higuchi.com introduces a free bookmarking service [ja] (in Japanese) called 4dk [ja], where bookmarks are visible only to those within a closed group. Higuchi refers to this idea as “group bookmarking”, explaining that it is different from the “group catharsis” of open bookmarking services like del.icio.us and Hatena bookmarks [ja]. The group bookmarking concept can be useful for closed work or project situations, where company information can be shared without fear of it being leaked, as well as for closed “mail-magazine”-style news.