I need your help with free nile decrypt tool. Is this tool in development?

Nile ransomware decryption tools are not in development - because only the hackers behind STOP/DJVU ransomware have the right decryption tool and keys for each victim separately. The security researchers have already analyzed NILE ransomware and, just like its previous versions, the encryption is extremely strong. That said, the only real hope to restore files is when someone with offline encryption pays the ransom, receives the key and this key gets uploaded to STOP/DJVU decryption tool by Emsisoft. You can always check whether this key is available either on the mentioned article or here: How to remove NILE ransomware virus.
Regards,
Norbert