It's called RAM Truth because it tells the absolute truth. System > Apps > Running doesn't properly break down RAM. It doesn't even distinguish between what's running and what's only cached.
Another good tool to get a good picture of what the OS is doing is System Panel:
But back to RAM...
RAM Truth gives complete usage results including Hibernating, Reserved, etc.
In RAM Truth tap on one of the memory listings for a pop-up with more details.
I'm using an app called NotiSysInfo, it's awesome and the notification widget looks awesome too! You can set it to show your Ram usage in the notification area so it's only one swipe away.