Microsoft Corporation.
App icon assets, which appear in a variety of forms throughout the Windows 10 operating system, are the calling cards for your Universal Windows Platform (UWP) app. These guidelines detail where app icon assets appear in the system, and provide in-depth design tips on how to create the most polished icons.
https://msdn.microsoft.com/en-us/windows/uwp/controls-and-patterns/tiles-and-notifications-app-assets

Essential graphics, visual indicators, and notifications for Windows Phone

Microsoft Corporation.
Keep in mind that on mobile platforms, simplicity is the most appreciable source of attractiveness.
http://msdn.microsoft.com/en-us/library/windowsphone/design/hh202884(v=vs.105).aspx

Windows 7 / Vista Icons (Aero) Guidelines

Microsoft Corporation.
Windows® 7 and Windows Vista® introduces a new style of iconography that brings a higher level of detail and sophistication to Windows.
http://msdn.microsoft.com/en-us/library/windows/desktop/dn742485.aspx

Creating Windows XP Icons Guidelines

Microsoft Corporation.
Discusses how to design and create colorful and dynamic icons for Windows XP using a vector program, such as FreeHand or Illustrator, and Photoshop.
http://msdn2.microsoft.com/en-us/library/ms997636.aspx

Apple Human Interface Guidelines (Aqua)

Apple Computer, Inc.
Describes the overall philosophy behind Aqua icons and shows how to design application, document, toolbar, and other types of icons for Mac OS X.
https://developer.apple.com/library/mac/#documentation/UserExperience/Conceptual/AppleHIGuidelines/IconsImages...

iOS Human Interface Guidelines (iPad/iPhone)

Apple Computer, Inc.
Beautiful, compelling icons and images are a fundamental part of the iOS user experience. Far from being merely decorative, the icons and images in your app play an essential role in communicating with users.
https://developer.apple.com/library/ios/#documentation/UserExperience/Conceptual/MobileHIG/IconsImages/IconsImages.html

Android Icon Design Guidelines

Google Inc.
This document shows you how to create icons for various parts of your application�s user interface that fit the style set by the Android UI team.
http://developer.android.com/design/style/iconography.html