Comment by gwern

A good wiki like MediaWiki supports various levels of visibility. For example, you could define a namespace for each group of readers like 'Family:'. Or use transclusions from subpages. (This might sound like a bit of a hassle but you can use a template to set it up once and for all: a page transcludes a public sub page followed by the distant relatives material followed by parents / siblings followed by your-eyes-only.) And I'm sure one could come up with other approaches too.

A real example: Said Achmiz (obormot.net) uses PMWiki for his D&D campaigns, and PMwiki lets you control who can see a page, so he can do access control tricks like a page for a location, where only the DM can see all subpages with all the secrets, while each player can see their own 'notes' subpage. So everyone in their own web browser can go to the same page and see the same thing overall, but will see just their private additional information. And this is quite flexible so you can encode whatever patterns you need. You don't need some WotC fancy custom CMS for your D&D campaign to keep track of information and silo appropriately, you just need a design pattern on wikis.