I saw a tutorial on this forum that wasn't very helpful as it was outdated and people still needed help. This is how you install Steam while running Kali 64-bit.
First thing you'll need to do is go grab the latest Steam.
You can find Steam on valve's official website:
http://store.steampowered.com/about/
Installation Instructions
You'll download a steam .deb file. Replace 'replace.deb' with your steam .deb filename.
Now that steam is installed, if you want to run Steam as the root user you'll need to locate /usr/bin/ and find a file called 'steam'.
Open this, and replace the following lines of code:
With:
Essentially replaced 0 with 1 in this file. This will disable that annoying root message.
If you're running a 64bit version of Kali and you're receiving a libGL.so error upon Steam's startup the following will fix that.
Now, reboot your system and run steam from the new desktop icon. Done!