Radare2 is a powerful reverse engineering tool for free. If you have a Kali OS, you can use it by default. But take care, the r2 version on kali might be 0.9.9, better to use versions newer than 1.2.0. You can check the version by
$ r2 -v. 0.9.9 sometimes cannot reverse the code correctly when comparing to 1.2.0.
Recomend installing from radare2's git repo
0x02 Get Started
$ r2 <filename> to open a binary file with radare2. Almost all instructions of r2 are reasonable and easy enough to remember and use.
You can type '?' to get help info.
Typical instructions are
0x03 Powerful Features 4 Beginners
V allow you to enter visual mode and analyse the code just like in IDA Pro.
$ r2 -c=H <filename> is an amazing feature allowing you to analyse code in web pages instead of cmd lines, this is useful especially for beginners who do not familiar with cmd lines.
Ok, I'm still learning. I'll update my blog when I learned more.