ASM

ASM is a simple symbolic assembler designed to use as little memory as possible. The assembler recognizes the official 6502 opcodes, can handle decimal and hexadecimal values, and allows for user-defined address labels and numeric constants. Not too bad for 8K with some room left over for programming.

The assembly syntax is a little unusual but I get the impression that some of the conventions we are used to today had not yet been standardized. You have to put your assembly instructions into BASIC DATA statements which are then parsed by the program and POKEd into memory. ASM comes with a sample program which you'll need to delete if you want to start writing your own. Deleting these lines is a bit inconvenient; it would have been nice to have been provided with a blank version of ASM.