Getting all running process and memory usage of downloaded apps

Apps like that aren’t really a thing on iOS. You may find them on other mobile platforms, but not here.

Consider this: such a tool would be useful only if you could get the name of each process executable (rather than, say, just a process ID). And getting that information would be a massive privacy fail. Your app would be able to infer (and make fingerprints of, and sell to advertisers) a list of what other apps the user has installed on their device. That sort of abuse is most definitely not supported by any API on this platform.

BTW, check out On Free Memory for discussion of why even aggregated memory information isn’t as useful as it sounds.