Kaitai Struct[1] is my preferred tool for parsing binary files. It's open-source (unlike Synalize It! and 010 Editor) and cross-platform (unlike HexFiend). Not sure how it compares to ImHex's pattern language, though—I've been put off by ImHex's UI the few times I've tried it.
My favorite thing about the Kaitai Web IDE is that it instantly updates the parsed tree as you make changes to the format specification, which makes it viable for reversing unknown formats instead of just specifying known ones.
My favorite thing about the Kaitai Web IDE is that it instantly updates the parsed tree as you make changes to the format specification, which makes it viable for reversing unknown formats instead of just specifying known ones.
[1] https://ide.kaitai.io/