Partitioning Software Is there an equivalent on the Mac platform to Partition Magic or GParted that will allow me to resize, move, and/or change partitions on the fly without formatting, or disturbing the data that is already on the disk?
iPartition (only ≤ OS X 10.13)
iPartition is now legacy. The company, Coriolis, finally closed in 2019. There is still a (now essentially freeware/donationware) version of iPartition available for download, but only good to OS X 10.13 for pre CoreStorage disks.
It allows you to move and resize partitions without deleting any data. It also works for Boot Camp volumes and other PC disks.

With iPartition, resizing a partition is as simple as selecting it, grabbing the resize handle and dragging. Not only that, but if you have several operations to perform, iPartition lets you queue them up and run them one after another, so you can have a cup of coffee while iPartition works. This feature, coupled with iPartition’s ability to automatically rearrange your existing partitions when necessary, makes iPartition the easiest partitioning tool that you’ll ever use.