The First Slice was a demo version of portal freely available to owners of Nvidia graphics cards as a small promotion. Here I have recreated the demo as a sourcemod since the original is no longer available. Why you would want to get a downgraded version of the game even though you already own the full game, I don't know, but here you are!
This is the standalone maps folder to be used with Source Unpack for speedrunners.
How to install:
1. Make sure you have Portal purchased and installed on steam
2. Extract the maps folder into your Portal Source Unpack folder (Source Unpack\portal)
3. Launch Portal.bat
4. Source unpack should load in with the maps added in