The best replacement for magento is oscommerce.

The best alternatives to magento are rated as following:
★★★★★  oscommerce
★★★★  opencart
★★★★  shopify
★★★★  wordpress
★★★★  prestashop
★★★  drupal
★★★  woocommerce
★★★  volusion
★★★  zen cart
★★  bigcommerce
★★  joomla
★  zencart
★  virtuemart
★  drupal commerce
★  wordpress ecommerce
  spree
  ubercart
  nopcommerce
  big commerce
  x-cart
  demandware
  drupal ubercart
  3dcart
  x cart

Your alternative for magento is not listed? Suggest!
Speaking about magento, one probably shouldn't forget about marketplace.

Other search terms related to magento and their ratings are:
★★★★★ marketplace
★★★★ varnish
★★★★ wordpress
★★★ redis
★★★ ecommerce
★★★ stripe
★★ cdn
★★ google checkout
★★ openerp
★ memcached
★ same id already exist
You have in mind a companion for magento and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of magento in all years. Click on graph for more.
magento
oscommerce
opencart