This is actually a really good manga, albeit a bit confusing at the start. It doesn't read at all like a normal manga. It's pretty much what the name obviously implies, a bulletin board for heroes, retired or active, to communicate, get help, vent and have fun. We have all kinds of heroes here, be it transforming "heroes"(like magical girls), people forced into it, random people who just fought a lot, maids, priestesses, priests, magicians, transforming robots, merchants, kings, empresses, summoned heroes, born heroes and even a demon lord summoned as a hero. They might be kind of average or might be ridiculously OP not bound by worlds at all. There are even detective heroes and people returning to be company employees or students, there are also people summoned over 20 times to other worlds to save them.
All in all, it's a comedy manga in the form of a sort of live-communication bulletin board where many of these heroes comes to vent because of their bad experiences and get help, support or just someone to listen amongst the other heroes. There we get weird stories about otherworldly adventures in f*cked up worlds, like someone accidentally summoned to an old-style game world, someone summoned to a world where the heroes role was to put the demon lord baby to sleep(literally) as only the hero could do so, a case where the female hero's companion is a narcissitic sword that goes around conquering all the women around her while complaining about the hero's lack of breasts.
There are many other events similar to that. It's essentially making fun of possible scenarios from hero tagged manga/novels/anime. There are all kinds of weird heroes around with screwed-up experiences. It's truly not a normal manga at all.
Anyway, it's a good manga. I feel like it'd be quite good even for people who aren't experienced with this "hero" stuff since the comedy is weird and screwed up even if you can't understand all the "in-jokes", it doesn't take a genius to understand why most of this stuff is amusing. However, there's still no doubt about this obviously being a fair bit more enjoyable if you're experienced with hero stuff, especially isekai manga/novels/anime. I'd recommend reading some of that stuff before coming back to read this for an enhanced experience.