Run the file through a service like VirusTotal before extracting.
If you downloaded this from a forum or a peer-to-peer site, check the comments or the "readme" file inside for the creator's name. pianoextra02.rar
The file appears to be a specific compressed archive that is not a widely known or officially documented software package, VST plugin, or music library in the public domain. Because it is a .rar file, it likely contains a collection of digital assets. Run the file through a service like VirusTotal