HTC has been on a roll releasing unlocked bootloaders for devices. The most recent being the 7 inch HTC Flyer courtesy of HTC’s development website. They have unlocked the bootloader for multiple versions of the Flyer including the international 3G and WiFi versions.
Before you head over to HTCDev.com you will need to know the version of the Flyer you own to be sure you get the correct firmware version. Also be sure you are fully up to date for the update tool otherwise it may fail. You can find the new firmware and update it at HTCDev.com on the bottom right of the unlocked bootloader list.
Now that you can unlock the bootloader it will allow you to install custom firmware on your pretty little HTC Flyer. Also take note that just because HTC offers the tools to unlock the bootloader that it still voids your warranty. Only do this if you are comfortable with how your device functions.