DiskDoubler was the biggest surprise for me, probably because I was least familiar with it. When I ran the "Text" test on it, all I could say was "Wow." No wonder Apple decided that a site-license for it would be a good thing. DiskDoubler fills a different niche than StuffIt and Compactor. DiskDoubler provides near-transparent file compression in normal use. Compress a document or application from the "DD" menu in the Finder. The document icon is then replaced by a copy with a little "DD" in the corner (only if DiskDoubler has been configured by Salient for that particular application). Weeks later when you need the document, double-click, and it (and its associated application, if that is compressed as well) is decompressed and opened. Quit from the application or close the document and DiskDoubler recompresses the document, and if appropriate, the application. Slick! Decompression wasn't quite as impressive as compression, but DiskDoubler took second place by quite a large margin nonetheless. The NuBus DoubleUp board (SE and SE/30 versions to follow) from Sigma Designs, currently in beta test, will make DiskDoubler up to ten times faster and may shrink the compressed files more as well.
DiskDoubler has no provision for self-extracting archives because it isn't trying to compete in the online compression battle between StuffIt and Compact Pro. Instead, DiskDoubler includes a freely distributable application and INIT, both of which can only expand compressed files. They aren't all that small, at 82K for the INIT and 96K for the application, but you only have to send them to your intended recipient once. If you regularly send self-extracting archives to the same person, sending DiskDoubler's free utilities is probably more efficient.
I have only two gripes about DiskDoubler. First, the progress window is a little obtrusive. I'd prefer a small, relocatable windoid. Luckily Salient has said they may include options for either a smaller window or no window in future versions to make DiskDoubler even more transparent. Salient also mentioned that although the progress window is modal, it does allow background tasks ample time. Second, there aren't enough icons included - the perfect solution would be an application that allows you to add icons from an application and put the "DD" in the corner - better yet, do it on the fly! (Thanks to Tom Zeller for loaning me a copy so I could review it - the only problem is I was so impressed that now I'm going to have to go out and buy yet a third compression program!)
Salient -- 415-321-5375 -- 800-326-0092
124 University Ave. Suite 103
Palo Alto, CA 94301
Salient on America Online and AppleLink
76516,1574 on CompuServe