pyz80 is a z80 cross-assembler written entirely in Python. It accepts text files with the syntax of the Sam Coupe's popular COMET assembler, and outputs a disk image suitable for loading in SimCoupe or transferring to floppy disk for use with a real Sam.
NasmSharp is an open source effort to build a x86 assembler written in pure C#. Primarily it is a C# port of well known x86 assembler NASM, written in ANSI C.
Involvement of some experienced C# programmers is highly appreciated.