lz4_reader-2.0.tar.gz

I might be way off but '.tar.gz' is a very common compression format. IIRC even WinZip or 7zip can decompress/unzip it. It might be that on the first run you'll get a .tar file (which is in cleartext anyway) but you can unpack that in a second run.

Oh I think you misunderstood the question. I was asking for the download link for this particular tool. 

oops, sorry that was a misunderstanding.

LZ4 compressor/decompressor is readily available here on Github or in a 7-zip version here 

I haven't seen the lz4_reader tool on the FTNT support site but I think it's not FTNT specific.

The first version was offered here in the past, but the log format has changed and is no longer available.

https://community.fortinet.com/t5/FortiAnalyzer/Technical-Tip-Transferring-historical-logs-from-a-FortiGate-hard/ta-p/193850

There seems to be an implementation that supports the new format, but even here we have confirmed that it cannot decode the latest FortiGate logs.

https://cyber.wtf/2024/08/30/parsing-fortinet-binary-firewall-logs/
https://github.com/GDATAAdvancedAnalytics/FortilogDecoder

We are hoping that lz4_reader-2.0.tar.gz will decode the current latest log format, but it seems to have a bug and is no longer publicly available.

https://community.fortinet.com/t5/FortiGate/Technical-Tip-How-to-convert-FortiOS-LZ4-log-files-to-readable/ta-p/372883

We eagerly await the latest version of lz4_reader-2.0.tar.gz.