No-one should need an undelete program. Proper backup procedures eliminate the need for such a tool with the exception of a file containing a lot of work since the last backup. Where I work we've had several inadvertent deletions which we've been able to correct by restoring the file from last night's backup.
A feature of the old DEC VAX operating system, VMS, (which I used in the mid 1980s) was the absence of the possibility of overwriting a file with a new version:
Every file had a version suffix consisting of a semicolon followed by a number. This suffix was invisible by default and a folder listing would only show the latest version by default. Every time you saved a file, its version number was incremented before saving and the previous version of the file was retained. There was a purge command which would delete all except the latest version or, if you wanted to keep a few previous versions, you could add, for example, "keep=3" to the purge command and the last 3 versions would be kept. This was particularly remarkable as it was in the days of expensive disc storage. It should be part of every operating system today when disc storage is both plentiful and cheap. A daily automatic purge could be set up to keep only the latest few versions to avoid accumulation of vast numbers of previous versions. Bring back VMS!