I have some ".rar" files on my Windows 8 PC and am curious how to unpack them to see what's inside. From a bit of Google work, it appears that they're archives of some sort kinda like a ZIP file. Help!

I'm a graphic designer and often have a dozen or more files that I'm working on for a client. When I need to check in with them, it's generally a pain because of the file count and they get confused by all the attachments and often don't unpack everything before calling me to say something's missing. Is there a smarter way to create a folder with my files on my Windows PC or some other archival approach I could use?

We have a situation where we need to keep a ZIP archive of some data files available on our Ubuntu Linux server so that our satellite offices can grab the information through slower data lines. Problem is, the underlying files change 2-3 times a day. What's a quick, efficient way to only rebuild the ZIP archive file on our Linux system if a file's changed, but leave it as-is if everything's stayed the same?