PSD file extension stands for adobe Photoshop document, Image file created by Adobe Photoshop program; a famous professional image editing Software.  But if you want to open or edit .psd image file without buying or installing Adobe Photoshop software. Here are a few tools to open PSD file without Adobe Photoshop.

Download and install free tools mentioned below, load the psd file in the installed program by going to "File" and then "Open.

It is an awesome free image and photo editor that makes photo editing more easily. To open and edit .psd file, you need to install additional psd plug in with Paint.net. Download Paint.Net

This  is free, small and simple tool that can open .psd files easily without photoshop.
Download IrfanView

Gimp is the GNU Image Manipulation Program. It is a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring. It works on many operating systems, in many languages.
Download Gimp 

Hope this helps you  ;)