The No More Ransom project website has free decryption tools for many known ransomware types.
The United States Cybersecurity & Infrastructure Security Agency (CISA) has a site with tips on how to prevent ransomware attacks.
If a decryption tool is not found, one option is to replace the hard drive and operating system and save the locked drive offline. A decryption tool may become available months later to free the data at that point.
iXsystems announced in March 2020 that TrueNAS CORE is the new name for FreeNAS, the popular open source NAS (Network Attached Storage) operating system. This was done to unify branding with its TrueNAS Enterprise product. Additional features were added to the TrueNAS CORE product as well. Documentation for TrueNAS is available at www.truenas.com/docs/hub/.