🚀 go-pugleaf

Assuming the use of rn as your usenet news reader:

> The features wanted are:  
> 
> 	Thread support -- Being able to follow a thread BOTH backwards
> 			  and forwards from ANY point.

use ^N,^P to move forward and backward through the same thread.

> 		       -- Begin able to save a complete thread into a
> 			  file from any point in the thread.

/pattern/modifiers:command{:command} is the command syntax so something like:
/SoftPC/:s softpc.file

This command finds all the articles with SoftPC in the subject and saves
them to the file softpc.file.

> 		       -- Being able to "FREEZE" a thread so that no
> 			  more notes can be posted to a certain topic.

use ^k which allows you to generate a kill file, which causes rn to skip
all articles of a given subject.  You would add a line to the kill file 
for the subject you want to skip such as:
/SoftPC/j

This junks (marks as read) all articles pertaining to SoftPC.

Typing h gives you help in rn.  This will show the above and other commands.