In a quick summary, it's Tumblr without content restrictions on porn. Tags, commenting without RT'ing, likes that aren't the same thing as RT'ing, the ability to "hide shares" so you can view just people's posts, a dropdown list of which "blog" to post from for people with multiple channels, and a dashboard display that's actually chronological.
But in more depth, it has the ability to embed HTML5 and CSS directly onto posts that make it onto the dashboard. Text formatting. Embeds from off-site that display properly and ask you if you want to allow the content or not.
Some examples of posts with their mascot, "eggbug":
First off, eggbug looks like this
Here's a game someone made of eggbug, directly embedded into a rebloggable post. https://cohost.org/pancelor/post/330039-hungry-eggbug
Here's a text post that I thought was an image but is just text formatting because hey that's wild. https://cohost.org/goatsnail/post/281807-div-style-font-2e
Here is a "useless box" that resets itself when you click it and I'm not sure if it's a CSS element or a flash animation or what but god damn. https://cohost.org/rosieposie/post/312281-useless-box
Here's a game that's just a page element that changes your cursor to different images to show states of eggbug where you keep eggbug as a tamagotchi. https://cohost.org/candiedreptile/post/64359-pet-eggbug-simulator
Eggbug text adventure as a rebloggable post.
It's sort of insane to see how much you can do and people already are doing with Cohost.
See how that last one is embedded directly into the post? You can do that with any link- even from off site. I just didn't do it for the others so this wouldn't be automatically turned into a readmore.
Made you look, #bozo.