EBay's ambitious project to turn its Selling Manager set of e-commerce tools into an open platform and repository of third-party applications reached another milestone on Monday when it was opened to the marketplace's sellers.

EBay vice president of Seller Experience Dinesh Lathi said in a blog post that merchants can now sign up for a free subscription to the new Selling Manager and give external applications that interest them a test run, since all fee-based applications have free trial periods.

Selling Manager has been around for years, amassing a user base of about 700,000 merchants, but it only featured applications built by eBay. In parallel, eBay has had a program for external developers since 2000 that has been joined by about 87,000 developers who have created about 13,000 applications.

EBay declared in June of last year its intention to remake Selling Manager into an application repository and platform open to external developers. After a months-long closed pilot, eBay opened the new Selling Manager to all developers in April of this year and promised it would make it available to merchants at some point this summer.

Besides, eBay hopes to boost developer participation in its platform with the new Selling Manager, while helping merchants more easily discover and access useful applications.