It's easy to extend Spree by writing your own extension. There are already over one hundred third party extensions listed in our official registry.
spree_fancy_theme Spree UI theme on both frontend and backend
spree_invoice_generator invoice generation of orders at both ends
spree_bootstrap_theme Bootstrap Theme ! Twitter-Bootstrap UI
spree_interakt spree extension to provide integration with Interakt application
spree_cpf Spree extension that adds brazilian CPF field in the address checkout form
Spree CSV Importer CSV Importer / Exporter
Spree Chimpy (MailChimp Integration) Spree/Mail Chimp Integration