Could you clarify if you are trying to to play on a Walkman, or if you are trying to extract files from an old device? Walkman - Amazon.com
There is no specific software or known project called "." It is likely a typo or a misremembered name for a utility that converts Walkman-specific media files to standard MP4 video or MP3 audio formats. Likely Intentions
If you are looking to convert files from or for a Sony Walkman, you might be looking for:
: There are niche developer tools on GitHub with similar naming conventions, such as slp2mp4 (for Super Smash Bros. Melee replays) or bag2mp4 (for ROS bag files), but none specifically named "walkman2mp4".
: Most modern digital Walkmans (like the Go to product viewer dialog for this item.