Which tool can you recommend for Vulnerability Assessment and Penetration Testing for an application built on the Microsoft Stack?

Hi peers,

We have developed an eCommerce system using the Microsoft Technology Stack. 

Now, we would like to perform Vulnerability Assessment and Penetration Testing (VAPT) of this system using a comprehensive tool. 

Can anyone recommend a tool that (preferably, an open-source one) to perform VAPT on the eCommerce application before releasing it to the client on production?

Thanks for your help!