What is the best free Mac cleaner

For Malware

Etrecheck

www.etrecheck.com

malwarebytes

www.malwarebytes.com

for any cleaning of the OS do not install any 3rd party utility. OS X is not Windows as does it's own cleaning far better than anything out there, and what's out there can cause serious problems. Avoid them.

No Anti-Virus software or so-called cleaning apps are needed or recommended for Mac OS. They can conflict with Mac's own built-in security. At best they will slow your Mac by using unnecessary resources and at worst will bork your entire system.

Etrecheck and Malwarebytes are exceptions. Use them if you suspect there is a problem with your Mac.

They serve different purposes. Etrecheck will only check your system on demand and needs interpretation to be useful. Malwarebytes runs in the background and will remove malware if it happens to be downloaded.

Such kind of software are not recommended neither usually useful.

Just use this: http://malwarebytes.com/ in the free version which do not install background processes.