Stand-alone up-rezing app for Mac?

[rbpeirce]

I used to have an Elements plug-in that did this pretty well, but I no longer use Elements.  Does anybody know a stand-alone app that will run on a Mac?

I did a dumb thing the other day.  I normally shoot RAW but decided to use JPEG for a specific application.  I forgot that when you select JPEG you also have to select image size and my camera defaulted to the smallest size, 1500x1000 pixels!

[rbpeirce]

I was told about Gimp, which runs on Mac and Linux and seems to be a non-Windows knock-off of PhotoShop.  It did a great job of converting my images to a larger size.