Oh my goodness yes. So much to love about !Zap. My first ARM assembly programs were written using the Zap disassembler/assembler extension. I also really miss the way it displayed search results, not seen another editor that does it quite like that.
Also on RISC OS "The Hacker" was one _the_ best ARM disassembler / OS inspection / debugging tools. It was sold as a game cheating tool, but was particularly great for pulling apart copy protection :) Learned so much with it. Again, still available, for an irrelevant OS.
(not that it's not still available, just that I can't justify working on a RISC OS system for the last ... 16 years :) ).