AppCompactor is a powerful tool which enables you to compress portable applications so they require up to 50% less disk space.
Why bother? If you're running an application from slow media, like flash drives or CDs, then you should find they now launch significantly faster. And the programs will decompress themselves automatically, so you don't have to do anything further - just launch your application and use it as you did before.
That's the theory, anyway. This kind of compression won't work with all apps, though, so you should back up your software first. But with that done, AppCompactor is very easy to use: just point the program at your portable installation's folder, choose your preferred compression method (or just select the default), and click Go. In just a moment you'll get a report on how much savings you've made, if any, and you can try the program out to see if you notice any increase in launch speeds.
Please note, malware authors also use this kind of tool to make it harder for security packages to detect them, and as a result antivirus tools may raise an alarm when they detect a compressed executable. AppCompactor is well known, though, so less likely to cause problems than most, but don't be surprised if a packed executable suddenly starts producing virus warnings. It's almost certainly a false alarm (though you should check it at somewhere like VirusTotal, just to get confirmation).