+ Assuming one knows what format a tape was made in, what is the easiest way
+ to list the contents of the tape?
Well, if you know what format they're in, that would imply you know what
command was used to write them... and all the tape-writing programs I know
have "list table of contents" functions.
+ If someone hands you a bunch of tapes and can't remember the format is there
+ any intelligent way to find out what format they are or just try tar, gtar,
+ cpio, ufsdump etc until you get a hit?
That /is/ the intelligent way. :-)
(Although knowing at least what platform created them may help, e.g.,
the byte-ordering differences between a Sun and an SGI machine will make a
big difference, if the tape was created on one and you're trying to read
it on another. Simply dd(1)'ing the stuff off of the tape raw onto disk
and /then/ experimenting with the disk file can also help, just because
you don't have to wait on the tape drive.)