Windows only: If your primary hard drive just isn't large enough to hold all the software you need on a day-to-day basis, then Steam Mover is the perfect tool for the job — assuming you have another storage drive handy.
Steam Mover was originally designed to help hardcore gamers move their downloaded games to other drives, in order to free up space on their primary hard drive. Cheap, huge drives came along and made this less necessary, but with the emerging popularity of Solid State Drives (SSDs), this needs to become commonplace again.
Steam Mover works amazingly well on games downloaded through the Steam client (which it was designed for), but as it turns out, it works well with other applications too. The program's target directory defaults to the applications folder for Steam, but simply change this to the folder containing the applications you wish to move. Once the folder is selected, all of the associated programs will be listed. Steam Mover works by moving all the data in the associated folder to your secondary drive; it then simply makes a link to the new folder you designate for the alternative folder. This means it should work on most applications.
Once you've got the target and destination folder selected, simply select the program(s) you would like to move. Click the right arrow at the bottom of the application, and soon the selected applications will be on the other drive. You can always move the application back to the original drive by clicking the left arrow.
It is important to note that this software is an initial release. The developer makes no guarantee that it will work flawlessly outside of transporting Steam games. In my testing, however, it worked very well, except for a small hiccup when transferring Illustrator and Flash Builder. The issue was easily resolved by copying everything in my new folder back into the original folder, however.
Steam Mover is a free download for Windows 7 and Vista. XP is not supported.