Detect how much RAM is available? (iOS)

I've never used this, but it seems to be what you need:

SystemInfo.system$$anonymous$$emorySize

http://docs.unity3d.com/ScriptReference/SystemInfo-system$$anonymous$$emorySize.html

Good stuff! I'll check it out. But how about free memory, i.e. memory that can be allocated by an app?

I can't say about iOS cause I haven't yet targeted iOS.

For Android this is the way I'd go:

Use either AndroidJavaObject or AndroidJavaClass to be able to call Java methods:

http://docs.unity3d.com/ScriptReference/AndroidJavaObject.html

http://docs.unity3d.com/ScriptReference/AndroidJavaClass.html

Then...

getRunningAppProcesses will get you a list of PIDs, and then getProcess$$anonymous$$emoryInfo will give you memory details about them.

http://developer.android.com/reference/android/app/Activity$$anonymous$$anager.html

Hope this helps.