The best replacement for fastboot is recovery.

The best alternatives to fastboot are rated as following:
★★★★★  recovery
★★★★  fastboot
★★★  bootloader

Your alternative for fastboot is not listed? Suggest!
Speaking about fastboot, one probably shouldn't forget about adb.

Other search terms related to fastboot and their ratings are:
★★★★★ adb
★★ unlock bootloader
★ android sdk
★ clockworkmod
★ sdk
You have in mind a companion for fastboot and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of fastboot in all years. Click on graph for more.
fastboot
recovery
fastboot