Large opcode support, including every documented Z80 instruction (and most undocumented ones).
Nested module code structure to break code up neatly.
Basic string-replacement macro preprocessor.
XML output of debug file and error log for emulators or IDEs to parse.
Extensive variables system allowing for variables to be 'typed' (as a debugger hint), including arrays and structs. Variables are shuffled around to fit in user-defined safe RAM areas, and temporary variables (that can be overwritten by other temporary variables in unrelated modules) can be defined.
Native output of raw binary, Intel (word), MOS technology and Motorola hexadecimal, TI-73/82/83/83+/85/86, and Sega Master System/Game Gear (including official ROM header and SDSC tag) files.
Simple multi-page application support.
...I also do requests.