The Amazing Awk Assembler (aaa) is a primitive assembler written entirely in awk and sed. It is quite slow, the input syntax is eccentric and rather restricted, and error checking is virtually nonexistent, but it does work. Furthermore it's very easy to adapt to a new machine, provided the machine falls into the generic "8-bit-micro" category.
pichart is a GUI for pigrammar, an assembler and programmer for picloader-programmed devices. pichart offers a user-friendly interface, making programming PIC chips easy. It looks like a flow chart designer and permits operations like reading from the device's serial port, writing on it, setting ports' value, and setting timers. It also permits programming directly during execution.
Erasm++, the Embedded Runtime Assembler in C++, is an Embedded Domain Specific Language (EDSL) in C++ for runtime code generation on Intel 64/IA-32 architectures. It supports complete compile-time syntax checking, and its code generators run very quickly because necessary data are computed statically. Also included are GenericDsm, a fast and generic instruction decoder library which supports "pattern matching" against the decoded instructions, and MetaPrelude, a Haskell-like lazy metaprogramming library that helps implementing EDSLs in C++.