Can be converted into an .exe file that extracts itself without needing the 7-Zip software installed.

daemondevin/7-ZipPortable: A portable build of 7-Zip ... - GitHub

Combines multiple similar files into a single stream to achieve even better compression.

There is no widely recognized software feature or specific public project named Based on the file extension, this is likely a private compressed archive created with 7-Zip software.

Uses the LZMA and LZMA2 algorithms to significantly reduce file sizes.