There are many memory / RAM cleaners. The ones I use I check with Task Manager and SysGauge, in both of which the visable reduction in memory usage is quite clear. The main ones I use at the moment are Memory Cleaner by Koshy John, Wise Memory Optimizer, IOB Performance Monitor and Smart RAM, plus also Glary Memory Optimizer and Synei RAM Cleaner --- the last one I have not tried because it is not free but Synei has the most thorough junk cleaner I have come across.
When I get warning notifications from Windows that memory usage is excessive the risk of crashing seems to be avoided when using a memory cleaner with a manual option. Two things concern me 1) why, when the cleaning effect seem to be quite clear (eg. in Task Manager) do some people claim they are useless (they may be, but the evidence suggests otherwise) and 2) why do I get memory shortage problems in the first place when I am told 4 GB RAM should be enough?
I dont know why some people have conflated memory cleaners with registry cleaners which are not the same thing and which I do not normally use.