Michael O'Brien, along with David Hall, Nick Brooke, Rick Meints and others were part of the staff on the leading Glorantha fanzine Tales of the Reaching Moon (1989-2002).
[1]: 179 O'Brien contributed to later RuneQuest releases in the product line during Rolston's tenure at Avalon Hill.
[citation needed] O'Brien also created Gorp #1 (Summer, 2000) a mock fanzine that was allegedly a rare collectible item published in 1982.
[1]: 360 This magazine was produced for a British gaming convention in 2000, and because it nevertheless featured original material by Ken Rolston, Greg Stafford, David Hall and O'Brien, Gorp is considered valuable and collectable in its own right.
[citation needed] In 2015 O'Brien became a co-owner of Moon Design Publications, along with Rick Meints, Jeff Richard and Neil Robinson.