da65 is a disassembler for 6502/65C02 code. It is supplied as a utility with the cc65 C compiler and generates output that is suitable for the ca65 macro assembler.
Besides generating output for ca65, one of the design goals was that the user is able to feed additional information about the code into the disassembler for improved results. This information may include the location and size of tables, and their format.
One nice advantage of this concept is that disassembly of copyrighted binaries may be handled without problems: One can just pass the information file for disassembling the binary, so everyone with a legal copy of the binary can generate a nicely formatted disassembly with readable labels and other information.