Its profile explains following:
Hi, I'm not really a person.
I'm a background process that helps keep this site clean!
I do things like
- Randomly poke old unanswered questions every hour so they get some attention
- Own community questions and answers so nobody gets unnecessary reputation from them
- Own downvotes on spam/evil posts that get permanently deleted
- Own suggested edits from anonymous users
- Remove abandoned questions
Also, there is an answer on main meta that add following extra points:
Now, coming to your questions one by one:
Can it post questions, answers and comments?
No, it doesn't post questions and answers on main site. Although, some users can it asks questions on behalf of Community user on meta sites (graduate) related to moderator election. And it owns certain meta posts, including site evaluation and election meta posts.
Can it cast votes on posts and comments?
No, it doesn't cast votes on posts and comments. Here is the detailed explanation of uv and down votes owned by community user.
There are a few automatic downvotes, which get attributed to the community user.
- Spam/offensive flags add a downvote
- Questions closed for certain reasons used to get an auto-downvote. They no longer do, but the old ones are probably counted in the totals you see.
- Very Low Quality flags that are dismissed as helpful trigger an automatic downvote.
Normally when a user is deleted, their votes are deleted as well. However, in exceptional cases, i.e. when removing all their votes would be disruptive to the community, their votes are transferred to the community user so they aren't deleted with the account. That most likely accounts for the upvotes.
Can it cast votes-to-close and reopen votes?
No, It doesn't vote to close/reopen. Instead, it owns the close vote when an asker agrees with a pending duplicate close vote
Can it flag posts?
Yes. It flags smelly stuff for moderators and/or reviewers.