The score_aln and score_aln2 applications are specialist ones which score *alignments* rather than structures.
Both score and score_jd2 score structures. The primary difference between them is their input/output options. score_jd2 uses the standard “JD2” input/output options that a large number of Rosetta applications use. The score application is an older application which has its own idiosyncratic input/output options. (Though most of the major ones match.)
The other practical difference is that the score application currently has better support for calculating rmsd. (Providing -in:file:native with the score application will result in rmsd columns in the output, though with score_jd2 it doesn’t necessarily.)