Software and apps like Senuke, GSA and Kontent machine are they even legal to be used. My friend said these software and apps are of part of black hat SEO, how true it is. Pls explain in detail.

Anything that attempts to take shortcuts to hard work is going to come back and bite you in the end. The problem is that automated sofware simply can't replicate the human element of deciding whether or not a specific backlink, etc., is truly relevant and the right choice, or if it's just spun content or the keywords match up.

There are many software's which makes your work easier than manual things. It might help you to rank up down, so its not a permanent.

Well, yes I would say some of these tools are part of black hat tools. They are going to help you in climbing you way all the top of the search result for a while but as soon as Google updates its searching algorithm you are going to move all the way to bottom of the ranking, and there would be a times when you will move out of the search results.

A gun is legal, till you use it to shoot somebody, then there is a problem. Getting a gun is a deliberate act the penalties are higher

The software is legal, The software may be used compliantly
when it is used non compliantly there there is a problem for the webmaster

Black hat for sure, anything that attempts changes in results carries huge SE penalties.
If the SEbots don't find it today, they will find it tomorrow or the next day, and de-list the site.
Follow google webmaster rules, or lose.