Fassem by Merlin (1984) is an extremely interesting and hard to find assembler / disassembler for the Commodore 64.  I spent hours just trying to find mention of this package and all I came across is two references.  One was from the magazine Commodore User Issue 16 (small sales ad) and a for sale listing at retrogames.co.uk.  This package is pretty unique because it lets you program in a type of BASIC syntax.  Check out the manual for all the details.

Big thanks go to BlueCursor for sourcing this truely rare program and manual.