NPCs

A number of NPCs (Non-Player Characters) wander the tower.

Interacting with NPCs

Emote to them. This might change their mood, as displayed in the close-up cam window. Different NPCs have different personalities, so the reactions to various emotes will vary from NPC to NPC.
Open trades with NPCs, and trade objects with them. Note that the player-NPC trade window is different than player-player trade: You have to drag what you want from their object frame (the extra panel) to their trade frame. They will show what they want from you by inserting greyed out items in your trade frame. If you give the NPCs a good deal, they will be more favorably inclined to you in a later trade.
Interrupt them: NPCs will pr. default walk around the tower on a semi-random route. If you click on them, they will stand still so you can interact with them. If you do nothing else, they will continue after 45 seconds.
Ask for task: Click on the NPC to target it and use "/whatsup" to get the task - the NPC will ask you to do something for it, and you can answer "yes" or "no" (plain text, no "/" in front) to the questions to accept or reject the task. Currently, just a small group of NPCs give tasks to players: Brandell (LabSpace), Callie (LabSpace), Kartik (RecSpace) and Masi (RecSpace)

An NPC is likely recognizable by the fact that:

they say "Yes" when selected, before they are even emoted to
their close-up cam shows a mood other than None
they tend to walk, not run
they respond to emotes almost instantaneously
their trade window is different for them than with player characters (as described above)

Unknown at the moment.

None at the moment.