PHProxyImproved was a high school project forked from the original PHProxy code. PHProxyImproved is no longer maintained and is free to fork under GNU General Public License.
Orgianly hosted under the google code website, the now defunt website is still in archive mode over at https://code.google.com/archive/p/phproxyimproved/
If you wish to download phproxyimproved, it’s still available at https://github.com/jeff142/phproxyimproved or forked under other authors on Github.
PHProxy improved is vary poorly coded, I actually learned PHP with this project and it was never meant to gain the usage it has, To my knowledge, there are no publicly published security flaws as long as the default password is changed. But looking back at this project, many best practices were not used, and I would not recommend using this software anymore.