I have some plans on making it easier to share games once PV8 is more stable. That being said, you should join the Discord server since it's a bit easier to communicate and there is a good group of people on there helping give feedback and sharing their work.
So there are save slots, each game has its own set of save slots. When you save a game disk it's saved to to a saves.json file. When you share a disk with someone else, they get your saved games too. I think I fixed the bug with SaveDemo and it should be working correctly in the next release. Finally, there are line drawing APIs but it's not very well documented. You can call NewCanvas(width, height) and then draw into that. It's hard to explain here but happy to help over discord and I'll be updating the docs.