Check if a user has an identical open question on another site before allowing them to post
6631
Can we automate detection of cross-posting?
142919
Is there a system in place to prevent new users asking, answering and accepting answers to each others' off-topic questions?
99295
How do you prevent a user from posting data multiple times on a website
295
Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?
118077
Provide indicator that another user is editing a post
47803
Answering the same question across the site
114583
Should users be allowed to remove the "Possible Duplicate" links on closed questions?
39711
Link up the excellent search engine that gives "Questions that may already have an answer" with the search box
140211
Move post to different user
105209
Auto-protect questions that get more than N answers from new users in a 24-hour period
151846
How do you search for questions filtered by a particular user?
80836
How to follow someone else's Stack Exchange (questions) filter
82853
Can Community ♦ raise a duplicate content flag when an answer is deleted and re-posted as a new answer?
127414
How was this new user able to post two questions less than 40 minutes apart?
16158
Is it legal to copy Stack Overflow questions and answers?
47837
Is it OK to crosspost Stack Overflow questions, now that the Portuguese SO is open?
23667
Build and strengthen the Stack Exchange community with "crossover questions" between sites