JooCart is released for OpenCart 1.5.3.1 with some important features.

NEW features done by OpenCart:
Company ID and TAX ID fields.
VAT number checking.
CKeditor updated to the latest .
Jquery updated to the latest. 
Voucher min/max limits in settings.

FIXED done by OpenCart:
SQL error in install
Bulgarian zones list is incomplete
more here http://www.soft-php.com/joomla-shopping-cart-system.html