Calypsi: A Cross-Platform Compiler Toolchain for Retro and Embedded Programming

Calypsi is a series of C compiler and assembly language cross-compiler toolchains targeting the retro and hobbyist communities. The current release (5.10) supports MOS 6502, WDC 65816, Motorola 68000, and HP Nut (assembler and debugger only) targets, running on various Linux distributions, macOS, and Windows. Features include ISO C 99 compliance, a fully reentrant code model, support for various data types, optimizing compilation, and a source code debugger. The toolchain is closed-source but free for hobby use; the HP-41 Nut target uses a BSD license, allowing commercial use.