Adam Harley (Kawauso)

A quick adaptation of the theme restriction code for widgets. Can only restrict on a site-wide basis, though it will only affect those sites on which it’s activated. Does not restrict super admins. Plugins must be active on the main site to be controlled by this plugin (this is an issue with WordPress’ plugin structure).
See also: <a href="https://wordpress.org/extend/plugins/restrict-multisite-plugins/" rel="ugc">Restrict Multisite Plugins</a>

Restrict Multisite Widgets

Allows network admins to restrict which widgets are available on sites, similar to themes.

Matthew Muro

Restrict Categories is a plugin that allows you to select which categories users can view, add, and edit in the Posts edit screen.
This plugin allows you to restrict access based on the user role AND username.

Restrict Categories

Restrict the categories that users can view, add, and edit in the admin panel.

Restrict Multisite Widgets vs Restrict Categories