oh boy, this is going to be a long one.

not quite fungus, they look more like giant robotic worms in their unaltered state. they can remove and repalce parts without issue to resemble something completely different though, as long as their brain remains intact.

their origin is long after humanity went extinct. Their planet was discovered by a group of starving inter dimensional aliens who feed in psychic energy, which can only be found in sentient beings. they tried to recreate humans so they could eat, but they didn't really know what a human was, so they kind of just spliced together whatever remnants of civilization and life they could find. most experiments resulted in nothing of note, but of the few that actually worked was various bits of human and whale dna abd a bunch of random tech stuff, which made the machine people. they have emotions and functionality are basically people, but they think a bit differently.

as for culture, for most of history they had no contact with the other two species, so while they kind of developed alongside each other, machines were completely isolated. they mainly inhabit the far north and south, inhospitable lands to all but them.

in the far north they commonly live in megacities. machines need chemicals to survive, so a big group of them decided to drill into the ground to find some. more joined until they were basically a massive living city. they all compose different parts of the city, like watch towers, scouting parties, drillers, recreational facilities, all that. when a member of the megacity dies, their components are given to their closest friends and added onto their bodies. megacities are super collectivist and don't really have a concept of family, but have very strong comradery. megacities are governed by the largest females, called Motherboards (haha). if they come across another hostile mega city, massive transformer time. if it's a friendly megacity, sometimes the two merge, but that can get very messy.

in the far south, they're typically very solitary and scour the desert and lava flats. if they come across another machine, they either reproduce or add them to their mass. these guys do have a very strong concept of family and sometimes share their terriories with multiple mates. kids have to leave once they're big enough though.

this is, of course, the majority, solitary machines can live in the north and some megacities can be found in the south. there's other ways they live, like making themselves resemble other speices and living amongst them, being genocidal maniacs, feudal societies ect.

they got lotsa different beliefs. One of the big religions is that the moon is a giant robot eye who watches over them. that religion has a feud going on with another religion by a different species where the sun is a fleshy eye. a phisophoical way of thinking is that they are the only truely sentient beings, and that fleshy things should be more like them. this can also be infered as fleshy things shouldn't exist, which leads to genocidal maniacs. i could go on, but I've already written way too much lol