Salesforce recently introduced a handful of new ways to show off your knowledge. Whether your expertise is in the Sales, Service, Marketing, Analytics or App cloud, Salesforce has a cert for you!
One of the new certifications will actually be one of the options replacing the previous Force.com Developer Certification. The new Platform App Builder Certification has very similar concepts and offers both a full exam and transition exam for those holding the older dev cert.
Now, for the transition options. The previous Salesforce Certified Force.com Developer exams are officially gone. (Previously obtained certifications are still valid and, as of now, recognized by Salesforce). Since these exams are no longer available, this means the new Platform App Builder Certification is the way to go if you are a functional developer.