Dolet for Sibelius 6.4 could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. We recommend checking the downloaded files with any free antivirus.
The actual developer of the free program is MakeMusic, Inc. The latest version of the software can be downloaded for PCs running Windows XP/7/8/10/11, 32-bit. The program lies within Multimedia Tools, more precisely Music Production. The most popular versions of the program 6.4, 6.3 and 6.2.
From the developer:
Dolet for Sibelius is a program that unchains your music by letting you save your Sibelius 5 and 6 scores as MusicXML 3.0 files. You can share your music created with Sibelius with people who use Finale. It lets you exchange the vast majority of information contained in a notation file, including rests, repeats, dynamics, lyrics, slurs, tempo marks.
You may want to check out more software, such as Sibelius Student, Sibelius or Dolet for Finale, which might be related to Dolet for Sibelius.