Customize Karbonn A21 with DarkBoid ROM By Santo_Rock

The new features obtained after installing new OS are listed below

• New Lockscreen
• New Toggles
• New Status Bar
• Added A lot Of Tweaks
• Support Init.d Tweaks
• Improved Battery Life
• Improved Touch Responsiveness
• New UI
• Added Trechubet
• New Google Search
• Added Apollo
• New System Background
• New Contacts And Phone Inteface
• Added Build.prop Tweaks
• Cleaned System
• Added New Bootanimation and Shut down animation *Surprise*
• New USB Debugging Sign
• Option To Theme ICONS
• Deodexed
• Zip Aligned APK's
• Improved Multi Tasking
• New Image While Tapping The Android Version Rapidly
• Added And Removed Apk's
• Etc......You'll Find Out!!

Souce: http://forum.xda-developers.com/karbonn-a21/development/rom-darkboid-rom-karbonn-a21-a9-cherry-t2071844

Procedure to install DarkBoid custom ROM

(Source for this section: http://www.celldekho.com/download-and-install-darkboid-custom-rom-for-karbonn-a21-karbonn-a9-and-cherry-mobile-flare/

• Download Darkboid custom ROM and place it into the SD card folder of your device.
• Make sure that you have ClockWorkMode installed on your device.
• Reboot your phone and boot it into Recovery mode by pressing volume up button and power button at the same time when the device is turned off.
• Navigate to mounts and storage > format system. Wait till the process gets completed.
• Now go back and choose the option of Factory Reset. This will finally wipe out your data and clear cache partitions.
• Find the option of Install from SD card, browse the memory and navigate to the file you just placed into your SD card.
• Select that file and then click Ok to confirm.
• After the process gets over, boot your phone normally.

This will make sure that DarkBoid ROM is installed in your device. Let me know if you have any issue installing this custom ROM, I will try my level best to solve all your problems.