One of the main platforms that I've seen across universities here in the US, is Piazza.
Piazza can be configured to allow students to post questions, answers and comments completely anonymously. There are classes where this works very well, participation rates are high and spam is rare. However, many faculty members, some because of unpleasant interactions in the past, often disallow anonymous posting.
Is there any research/anecdotal evidence that suggests anonymity hinders / helps learning? In the latter case, are there specific steps used on anonymous fora that are required to maintain quality? We're planning on building a large QA-system within our EdTech platform, and on the fence about investing thousands of dollars to build "anonymous posting" within our system.