When you edit a document, some software will generate automatically a new version of the document and allow you to see what changed. If the software is sufficiently smart, you might even know when and by whom the change was made. Wikipedia is good at keeping traces of everything. Email and blogs leave traces. Videoconferencing does not usually leave traces: you cannot replay a Skype conference after it has concluded.
However, beyond keeping traces, software can share and index traces. Each email is a trace of a conversation, and it can be retrieved later, but your emails are not shared. Word processors allow you to send a document with recorded changes, but you cannot easily refer to a specific change in the document.
In any case, I made the following table:
|Medium||Keep history||Share history||Index history|
|Phone, Videoconferencing (Skype), face-to-face||No||No||No|
Credit: This idea came after a discussion with Sébastien Paquet.