xtail watches the growth of files.
You can specify both filenames and directories on the command line. If you specify a directory, it watches all the files in that directory. It will notice when new files are created (and start watching them) or when old files are deleted (and stop watching them).
The version 2.1 release fixes a Y2K bug, replaces the fixed-length file list with a dynamically allocated one, and implements package configuration with GNU autoconf.
The xtail program has been around for a long time. O'Reilly & Associates even included it in their Unix Power Tools book. A link to the 1989 release is included below. The 3B2 sitting in your cellar would love a copy.