PHProxyImproved was a highschool project forked form the orginal 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 PHProxyImproved is no longer maintained, and is free to fork under GNU General Public License.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, its still avable 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 is no security flaws as long as the default password is changed.