The first version of the Sharp SM-5 assembler is released and seems to work pretty much okay. It is one of the links on the right.
It comes in a zip file with a demo source file and an assembled binary file. To run it just run java -jar sharpasm.jar demo.asm and it runs and assembles a file demo.bin. It always produces a 2,816 byte binary file as output.
Source will be released later on, likely at the end of the Retrochallenge sometime. It's very much version 0.1 at the moment, though I think it works.
L8R: Minor update to v0.11, missed something silly out.