iBored

iBored is basically a hex editor for disk sectors, but can also be used to edit files, including disk images. iBored comes with hardly any documentation, and it doesn't explain what it does, either. If you have not used other tools to edit disk blocks or files on a binary level before, you may find it difficult to use. Can access disks remotely over a network connection. It can save a range of blocks to a file and write a file back to disk and has a powerful template system to view and analyse disk structures. It can edit MBR and GPT partition tables and install a PC BIOS bootloader dealing with both MBR and GPT.