iRamDisk uses a part of your RAM to create a new volume shown as an ordinary drive that can be mounted and used independently in your Finder.
Since the access time to these datas is way more faster than usual (it can reach over 10 times of the normal speed for some configuration), it lets you do some things you would not be able to realize with a classic hard drive (along with relieving your internal one) such as getting a writing speed amazingly fast or moving the temporary files of some apps (Safari, Xcode,...) over it when you want to optimize their own access time along with minimizing the impact of these files on your SSD.
However, do not forget that your computer does not have as much of RAM as your disk space and that you will lose the data placed on the new volume when you restart it. So, be careful when using it!
What's New in Version 3.5.4
Update 3.5.4 disables function on El Capitan
I’ve been using this for years, to cache browser activity. I had it set to cache /Library/Caches but it no longer worked on El Capitan, and caused problems with errors on system shutdown.
Unfortunately, the author updated it and disabled the ability to use it to redirect the /Library/Caches files, so it is only useful now for Safari cache and for general ramdisk use - it is no longer useful as a general-purpose cache or mac speedup tool.
Mac App Store: https://itunes.apple.com/us/app/iramdisk/id492615400?mt=12