PuTTY is a terminal emulator available for Windows, Linux and OS X. While it’s not available for Chromebook, there are some alternatives to check out.
If you’re looking for PuTTY you’re probably comfortable with poking around under the hood. Know this – Chrome OS is built on top of Linux, and has a crosh terminal you can use right now. If you’re looking to SSH somewhere or just ping something, it’ll do just fine. You can get to it by just hitting CTRL+ALT+T, which will open a new tab running your terminal.
If you need something with more power and more features, Google produced the Secure Shell app. It’s only terminal emulation, so you can’t use it to access your local Linux prompt, but if you’re connecting to something remote it’s just what you need.