The utility, yfolder.exe, will pretty much show you threads in a folder,
since it lets you sort messages by Subject (or other criteria). After
the sort you get blocks of messages with the same subject, that would
have been displayed as threads in a newsgroup.
yfolder also has another handy feature, sorely lacking in yarn itself:
It lets you mark several messages in a list and do some operation like
copy to a file or folder to the whole group of marked messages, instead
of having to process messages one at a time like yarn makes you do.
yfolders interface is very similar to yarn's. It is part of the package
included with YES - the yarn editor shell -- which is mainly intended
to manage signature test at the end of each mail sent out.
Hope this helps.