Our team has just published the third Beta version of PrestaShop 1.4. Numerous new optimizations are included, improving our future flagship version 
- Optimization of many modules: BlockCMS; One Page Checkout, Guest Checkout; Sponsorship
- The module GridExtJS, deprecated, was removed from the solution
- Improved WebService
- Optimizing imports from OsCommerce
- Improved product page in the Back-Office
- Better management of the Eco-tax
- Optimization of the search engine on the "Modules" page in the Back-Office
- The module GridExtJS, deprecated, was removed from the solution
- Improved WebService
- Optimizing imports from OsCommerce
- Improved product page in the Back-Office
- Better management of the Eco-tax
- Optimization of the search engine on the "Modules" page in the Back-Office
The complete list of modifications is available in the CHANGELOG.