Right, I should have put that in resources. It's pinned in our discord but if you don't wanna join then here you go

https://drive.google.com/open?id=1uvhB4VEOPK1OngRuxD4YslAVztaEVpG8

You can; I doubt online would work, but you can download older versions from SteamDB (https://steamdb.info/depot/382561/manifests/ assuming Windows).
There are a lot of guides explaining how to use it, so I won't go into further detail here -- Google "downpatch steam game steamdb".

The Site

Hot Lava

Portal 3D

Deltarune

Is it possible to play a old version?

Is Japenese faster than English to speedrun?

Where can I get the game?

Can't change avatar!

nhaar

pisschilling

SEUM: Speedrunners from Hell

coop_mission_haunted

coop_mission_rage

coop_mission_storm

FrostRunner

Portal 2 Bhop