Doujinshi event Comitia is held four times a year, with its largest edition scheduled for Golden Week at Comiket home venue Tokyo Big Sight.
It’s not strictly manga, with other creative efforts being presented, but, unlike Comiket, there’s no cosplay, no company/anime promotion, and no parody works.
And, maybe not completely true to the spirit of the event, he posted a GG parody of the experience.