All HTC Android smartphones launched after September will be supported by official HTC bootloader

Currently, the HTC developer site has a list of 10 devices that can have the bootloader unlocked. This list includes popular HTC models such as EVO 3D, Flyer, Sensation, Sensation 4G,  Amaze 4G and myTouch 4G Slide. Newer handsets such as Sensation XL, Rhyme and Sensation XE are not listed as suppored but this will change soon as HTC now announce that all Android devices launched after September 2011 are unlockable using the HTC tool. Some older Android devices launched before September will also be unlockable but HTC has not announce which devices this will be. It could be Desire S, Incredible S and Wildfire S which are some of the models announced earlier this year.

The bootloader is a small program that decides which application must run in the startup (boot) process. By unlocking the bootloader, the user can customize software on the Android device. More on the unlocking process

source, via