How is Mojarra different from Sun's JSF Reference Implemenation?
Is it just a later version? Is it simply a rename?
The Sun JSF Reference Implementation, also known as Sun JSF RI, was named like that, just "JSF RI", from the beginning on (2004) until version 1.2_08 (2007). The dev team found "JSF RI" a boring and nothing-saying name and would like to give it a bit more identity and recognition. They wanted to have it in line with the "Glassfish" project which JSF RI is part of. After some user community polls (initiated by the good ol' forums.sun.com), the name "Mojarra" was been chosen. Since version 1.2_08, the name "JSF RI" has been replaced by "Mojarra". But it's essentially the same implementation. In other words, Mojarra is the JSF Reference Implementation.
Later, when Sun was taken over by Oracle in January 2010, the company name "Sun" was obviously replaced by "Oracle". And yet later, when Java EE was reowned by Eclipse instead of Oracle in September 2017, the "Java EE" project name was renamed to "Jakarta EE" (for legal reasons because Oracle owned "Java" trademark) and the company name "Oracle" throughout Jakarta EE was replaced by "Eclipse".
Later, with the release of Jakarta EE 10, the spec name "JSF" was renamed to "Faces" in an effort to de-acronymize as many as possible abbreviations within the Jakarta EE umbrella for clarity.