This is a meta-issue to cover in-world, primarily short-distance communications and state sharing between scripts, between custom viewers, and between scripts/objects and custom viewers. There are a plethora of special purpose communication channels, both obvious and otherwise, that components of systems can use to communicate. There's no overall communication design, so you have llInstantMessage for communicating between objects and avatars, llSay(and friends) and listens for broadcast communications, and link messages for broadcasts local to a linkset. What we don't have are point-to-point messages between objects, point-to-point or broadcast messages between viewers or between viewers and objects, or passive information sharing between object or viewers. This meta-issue is linked to a variety of proposals for in-world script-view-agent communications.