Oscommerce can be modified to work on PHP 7, taking advantage of PHP 7’s increased security and speed.

Work is in progress both on the current stable Oscommerce 2.3.3.4 and the new up and coming Online Merchant v2.4.0 Joli.

The community version is the closest to being fully compatible with PHP 7 as of the time of writing this, and it has its own PHP 7 compatibility branch on Github that is more or less ready to run on PHP 7.

Resources:
– osCommerce
– GitHub osCommerce Responsive Community PHP 7 Compatibility Version