Activity
Who did what, across the workspace and on each post.
The workspace feed
Activity in the sidebar lists what's happened in the workspace, newest first: posts scheduled, rescheduled, published or failing, approvals requested and decided, campaigns created, and the rest. Filter it by kind to find, say, every post that failed this week.
A post's history
In the composer, open Info and scroll to its activity. It shows the post's whole life: when it was created, each round of edits (with which channels changed), title, tag and campaign changes, every scheduling move, every approval step, and when it went live.
Edits are grouped: a burst of typing by one person shows as one line rather than a hundred, and a change that's undone straight away doesn't show at all.
Audit log
The audit log records security-relevant changes, such as members and roles, API keys, integrations and billing. It's part of the Advanced plan, and its page in Settings is coming soon.