Windows Mobile
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This page collects some useful resources for working with Windows Phones.
Tools
WindowsPhoneInternals[1]

WPInternals by an XDA-User allows you to perform tasks like unlocking bootloaders, enabling root access and flash or backup firmware. Some fixes have been made in the GitHub repository, but no new release has been made yet. The list of supported models on the official site is outdated. The the image on the right for a list.
Windows Device Recovery Tool[2]
The Windows Device Recovery Tool by Microsoft let you recover firmware of Windows devices.
Projects
Android4Lumia[3]
Android4Lumia is a project which aims to built android based custom roms for Lumia phones.
File Collections
LumiaFirmware.com[4]
On LumiaFirmware.com you can find firmware for Lumia Phones.