I have noticed that my free software hex editor (hexxed) – which is licensed under the GNU GPL – does not really come up in any searches, so here’s another entry to boost it.
It’s a bit crude, but it does some things well (e.g., display unicode and switch endianness) and it will run anywhere you can get Java to work. And as it is free software anyone is free to make it better.
This page tells you all about how to get it and use it.
cartesian product ... stuff about computing mostly 