Does an iPhone need a ram cleaner? If it does, which one is good and free?

RAM cleaners are a ridiculous concept that does more harm than good.

On any modern operating system, and in particular any UNIX system like OS X, iOS and Linux, it's typical and expected to have the whole memory as full as possible. The RAM is used for caches and buffers, both for apps as well as for the operating system. The operating system and most apps are well designed to take advantage of this.

A RAM cleaner is simply an app that will request as much memory as it can from the operating system, kicking all those caches out and invalidating all the effort from the other stuff buffering and caching stuff. Sure it looks like there's more free memory after the operation, but then anything you do will be much slower.

Running a RAM cleaner is like cleaning up the whole kitchen in the middle of doing a meal. You light the grill, and then before putting the meat, you'll turn the grill off and clean it up. Waste of resources. Sure from time to time it's a good idea to cleanup the kitchen, but surely not when you are using it and when you've spent already effort cooking stuff.

More details:

With Java there is no way (to my knowledge) to let the OS inform an App to "clean up". Sure there are the WeakReferences and SoftReferences that allows stuff to be lightly bound and let the GC clean it up if it needs memory, but that's not something that helps the App have some control of the stuff.

With iOS there is a specific "message" that the OS can send to the apps and tell them "clean up some memory, or else I'll kill you". Apps can then apply whatever measure they need to reduce their memory footprint. If the app doesn't implement it, or doesn't clean up enough memory, the OS will simply kill the app. Apps on iOS shall be designed to have the same experience both if launched from cold as well as if re-focused whilst already running. (not that all apps do that).

So a RAM cleaner on iOS doesn't do anything else than the iOS would do - first ask all apps to cleanup memory, then consume enough memory to force the apps to die, then force the OS to remove all caches and make the device as slow as if it was cold restarted.

A RAM cleaner on Java kind of works not because of it's own merits, but because it's a good way to kick out apps that are badly implemented and miss-behave on the memory consumption. The end result is exactly the same as if you'd manually kill the app. Maybe it does help on the OS, but I strongly hope it doesn't, or else it would mean the Android OS would have some serious issues.