I was able to use the Wayback Machine to get the complete walkthrough for this game.
You must be registered to see the links
Just ignore the large icons and pictures at the top of the page and scroll all the way down to the bottom until you get to the text walkthrough.
Controls:
WASD: Move
Space: Jump
Shift: Sprint
E: Interact
I: Inventory (and Journal)
N: Speedhack
Sometimes to proceed in the game, instead of pressing E on your keyboard to "Use", you need to stand in a specific area, open up your Inventory, select the relevant item, and click the in-game Use Item button.
Ctrl is supposed to let you dive deeper while swimming. I haven't tested it. When I was swimming, I just quit pressing keyboard buttons and that let me sink below the surface.
There are some other controls like X and Z, but I saw some comments about how you shouldn't use them because they might break the game.
There is no Save or Load Save in this game, so you have to play it from beginning to end without exiting or breaking the game.
If you plan on deleting the game after you are done playing and want to erase all of the game files, you can delete this folder afterwards.
C:\Users\UserName\AppData\Local\OST_Game