Apple has instituted new security measures for downloads and only recognizes apps sold through the App store by default so you may have to adjust your security settings to open the demos.
If you want to try the demo (and you trust Prosanity) but are having problems opening the files here are the steps to open the programs after downloading:
1. Go to System Preferences in under the Apple menu in the upper right corner of your screen.
2. Select Security & Privacy in the Personal first row.
3. Under the General tab, click the lock in the lower left corner to unlock the setting. You will be prompted to enter your computer password.
4. Select Anywhere as the second Option for Allow applications downloaded from.
5. Now you can open the program.
After opening the program, you can reset these settings if you like.