waht is crucial macscanner

Please provide some context as to you question.

If you are asking about anti-virus software or cleaning software, there are none that are crucial. All should be avoided as certain programs actually cause problems.

NEVER download MacKeeper, CleanMyMac or similar as they are damaging malware.

Crucial System Scanner

It is a tool from Crucial that you or someone downloaded to allow Crucials web site to scan your hardware so that they can recommend upgrades. If you don't want it just drag it to the trash and empty. It's harmless.