Upload a Premiere Project (.prproj) file and this tool will instantly convert it to be openable in any older version of Premiere.
Your file will automatically download upon clicking Convert.
A Premiere project (.prproj) file is basically an xml file wrapped up in gzip compression. One of the nodes contains a version number corresponding to the version of Premiere which created it. Premiere checks this when opening a file and refuses to open anything with a lower version number, even when the project is basically compatible: "This project was saved in a newer version of Adobe Premiere Pro and cannot be opened in this version."
This tool simply changes that version number to '1' and creates a gzip compressed file which Premiere can read. You can perform the same process yourself manually, as described here, however this tool makes it simple.
Because this is a cheat, some filters and effects may be lost when converting.