[Windows 10 Mobile] Windows Blue:
First of all, use this thread at your own risk.

If you decide to give it a try make sure your smartphone has a SD Card slot otherwise this will not work and it's best to use this on a secondary device because there is always a chance that you have a critical bug and a hard reset is necessary to restore your device.

Also 512MB RAM devices are not supported, so only use this tutorial if your device has 1GB or more RAM.

There is already a thread on here from jimmy19990 that explains how to do this but it seems that people with less experience in this department do not understand it completely, so I decided to put all the steps in this thread:

1. (skip this step if you are on Windows Phone 8.1) If you already upgraded to Windows 10 Mobile make sure you go back to Windows Phone 8.1 with "Windows Phone Recovery Tool" or "Lumia Software Recovery Tool" which you can find here:

http://www.microsoft.com/en-us/mobile/support/faq/?action=singleTopic&topic=FA142987

2. Backup your files on your SD Card and format it in Windows Phone 8.1 (settings < storage sense), if you get a message that asks to save new files to the SD Card click no and check in storage sense that new files are all saved to the phone, not the SD Card.

3. After this download and install the "WP8.1 SDK Tools Lite Setup Av1.20" from here:

http://www13.zippyshare.com/v/15281796/file.html

4. With "WP8.1 SDK Tools Lite Setup Av1.20" installed you will have "Windows Phone Developer Registration 8.1" (start menu < Windows Phone SDK 8.1) open this and register as Developer.

5. Go to the app store on your phone and search for "Preview for Developers" and install this app, move it to the SD Card with storage sense (settings < system < storage < phone < apps & games) select the app and tap "Move to SD Card".

6. Now download "CustomWPSystem_0500.xap" from this thread:

http://xdaforums.com/windows-phone-8/development/xap-customwpsystem-patch-xaps-wpsystem-t2975419

7. Connect your phone with a usb cable to your computer.

8. Under "Windows Phone SDK 8.1" is another program called "Windows Phone Application Deployment 8.1", open it and click "Browse", navigate to the "CustomWPSystem_0500.xap" file and click "Deploy", after a while you get a message that it succeeded.

9. Download "CustomPFD_0003.xap" from another thread:

http://xdaforums.com/windows-phone-8/development/xap-custompfd-registry-editor-tweaks-t2981057

and copy "CustomPFD_0003.xap" to the root directory of your SD Card.

10. Take your phone and open "CustomWPSystem", tap "SD Card permissions", click on "sd card" and press the checkmark.

Now tap "Select the XAP" (at the bottom of the page in "CustomWPSystem"), navigate to "sd card", select "CustomPFD_0003.xap" and "Apply XAP".

Wait till you get a message "Operation Completed".

11. Close the "CustomWPSystem" app and open "Preview for Developers" app (icon will be changed), go to HKLM\SYSTEM\Platform\DeviceTargetingInfo and change these values (just open for example PhoneSOCVersion, put 8974 in the textfield, press "Write", back button and go to the next one):

For a Full HD (1920x1080) device:

PhoneSOCVersion: 8974

PhoneMobileOperatorName: 000-GB

PhoneManufactorModelName: RM-937_eu_euro1_231

PhoneModelName: Lumia 1520

OR

For a HD (1280x720) or lower resolution* (800x480 / 854x480 / 960x540) device:

PhoneSOCVersion: 8926

PhoneMobileOperatorName: 000-HK

PhoneManufactorModelName: RM-984_1000

PhoneModelName: Lumia 830

*On lower resolution devices the interface will be a bit smaller as normal after the registery edit, but as soon as you complete step 14 your original device info and interface will come back.

12. After you changed your info to one of these devices, go to the app store, search "Windows Insider" app, install it and open it.

13. Sign up for the Fast Ring and check for updates, you will receive a message that "Build 10.0.10536.1004" is available, let it download and install (will take around an hour or more and the device will reboot itself a few times).

14. Once Windows 10 Mobile is installed do a hard reset (settings < system < info < factory settings) and let it format the SD Card also. (this will also take about an hour or more)

15. Now you will have back your original Device Info and in windows < system32 < aow will be the necessary files to run Windows Bridge for Android.

The following steps are to actually install an APK on Windows 10 Mobile:

1. Download Visual C++ Redistributable Packages for Visual Studio 2013:

http://www.microsoft.com/en-us/download/details.aspx?id=40784

download and install "vcredist_x86.exe" and "vcredist_x64.exe".

2. In this thread you will find the new files for the "WindowsBridge.7z":

http://xdaforums.com/windows-10/windows-10-mobile/fix-fix-android-applications-installing-t3202036

Extract "WindowsBridge.7z" and install "IpOverUsbInstaller".

3. Here you will find the installer to deploy the APK's to your device (Download Version 1.3.1 Here / minimal_adb_fastboot_v1.3.1_setup):

http://xdaforums.com/showthread.php?t=2317790

Download and install.

4. Turn off your lock screen (settings < personal settings < lock screen), time-out: never.

5. To enable developer mode on the phone and to find it in the network:

First find your ip adress from the phone: settings < network and wireless < wi-fi and press your network, type your ip address in a document.

Then go to settings < update & security < for developers, press "Developer mode" and tap "Yes".

Turn on "Device discovery" and press pair.

6. Open your map "WindowsBridge" from step 2, copy the directory and open an elevated command prompt (run < cmd < right-click < run as administrator).

Type "cd" and paste the directory of the "WindowsBridge" map (example: "cd C:\Users\User\Downloads\WindowsBridge".

After this type "wconnect.exe" and copy paste the ip adress from the document in step 5 and press enter (example: wconnect.exe xxx.xxx.xxx.xxx).

Enter the pin you see on your phone, wait a while and it will say "connected".

7. Now download the APK you want to test with this link (just search the app in the Google Play Store, copy the link and paste it in the website below):

http://apps.evozi.com/apk-downloader/

Cut and paste the app to C:\Program Files (x86)\Minimal ADB and Fastboot and copy the directory of this map.

8. Go back to your command prompt type "cd" and paste the directory ("cd C:\Program Files (x86)\Minimal ADB and Fastboot")

9. Type "adb install" and copy and paste the name of your apk with the .apk extension included ("adb install test.apk").

10. Wait a few minutes and there will be a message "Succes", now on the phone press "Abort" and "unpair all", your APK will be installed.

I tested this method with a Lumia 640, used the Lumia 830 device info and it works like a charm.

Thanks to all the threads and websites I mentioned, because all these tools make it possible and easier to run this project.