I recently went into need of a HEX Editor. After a bit research, I got to know some of them actually could disassemble binary files and some even enables you to re-assemble parts of them.
The second feature is looks really fascinating. Though I found only two of them which could do this. First is HIEW aka Hacker's View and second is HT Editor. Former is shareware and later is open-source. Unfortunately both have DOS based interface. I really liked HIEW because of the features they give are really good, particularly assembling. But HT Editor is free and could assemble too. Both supports a wide variety of executables including x86-64 assembly. You can look at their webpages for the features they offer.
HIEW probably is more popular and favorite. It could also show induvidual bytes, words, dwords binary which is a useful feature. On other other hand HT Editor gives you regex search feature.
More difference you could see when you actually get them into use.
Also, I would just like like to list three other hex editors called BIEW, QVIEW and HexIt. All support various formats and processors. They all have DOS Based UI and disassembler. BIEW I think is best. QView is a bit old and outdated now but, it has disk editor and jump tracing feature.
You could also find good comparision of Hex Editors here at Wikipedia.
