I'm using a Mac.
Thanks for letting me know!
I went through on my MacBook and was able to open and run the game successfully. Here's what I did, step-by-step:
1. Go to the downloads page, and Download the 2nd file (the one with the apple icon at the very right) that is called 'A-Day-in-the-Life-of-a-Slice-of-Bread-1.3-mac.zip'
2. Double click on the zip file to unzip
3. Open the unzipped folder by double clicking
4. You might get a prompt that says "A Day in the Life of a Slice of Bread" is an application downloaded from the internet. Are you Sure you want to open it?" and select "Open"
5. If the game does not even open, go to system preferences > general > click the lock to make changes > enter your password > and where it says 'Allow apps downloaded from' make sure "Anywhere" is selected.
6. Once you have done that, reopen the game folder and double click on the bread icon to start the game.
I think that might solve your problem! If it doesn't, please let me know :)