Crush is an open source tool in Golang developed by the folks at Jemurai to essentially accelerate code review projects.
The bottom line is that you could do the same thing with a set of regular expressions or grep. So how useful is it? Not very.
Since it doesn’t parse the code into an AST (like code analysis tools) it has limited knowledge about what the system really does. As such, the findings it produces are just candidate issues.
Crush does have some interesting automation capabilities, like being able to diff sets of findings (which is really part of fkit). But nobody actually uses fkit and if you get this far, you might as well write your own in Perl or Python or Ruby or whatever language you prefer.
Recommendation: use if you do code review and you like it but ignore if you have better options.