IFEFFIT is an interactive program and scriptable library for XAFS analysis and FEFF fitting. It combines the core algorithms of AUTOBK and FEFFIT with general data manipulation and interactive graphics into a single package. IFEFFIT is available as a command-line program that can be run interactively or in batch mode, and provides a library of functions usable from C, Fortran, and high-level scripting languages like Tcl, Perl, and Python. A graphical user interface (GUI) is demonstrated for rapid 'online' data analysis. IFEFFIT is freely available under an Open Source license, encouraging outside use, development, and contributions. The introduction highlights the importance of high-quality, easy-to-use programs for XAFS data analysis. Dimakis and Bunker's APEX program demonstrated the feasibility of such a program. IFEFFIT aims to provide robust EXAFS analysis procedures and a facility for users to write macros, scripts, or programs for repetitive tasks. It also emphasizes the need for form-based GUIs, predictability, and uniformity in analysis procedures. The command-line interface allows users to read, write, and manipulate data, including XAFS analysis procedures, Fourier transforms, and FEFF calculations. IFEFFIT supports data manipulation and plotting, and data is stored as one-dimensional arrays. It supports basic mathematical operations and has a simple command-line interface. The programmer's interface allows IFEFFIT to be used from Fortran or C programs, and also from high-level scripting languages. The IFEFFIT library provides seven basic functions for accessing the underlying "IFEFFIT session" and its data. The principle function, ifeffit(), executes IFEFFIT command strings as if they were typed at the command-line. G.I.FEFFIT is a graphical interface built using Python, providing forms for common analysis tasks like data reading, plotting, and XAFS analysis. It is still in development and lacks a complete form-based interface for FEFFIT-type fitting, but is a flexible program for simple data processing, plotting, background subtraction, and Fourier transforms. IFEFFIT is free software, distributed under an Open Source license. It is in an early stage of development, though most algorithms needed for XAFS analysis are supported. It lacks some advanced features like simultaneous fitting of multiple data sets and improved background refinement, but has many capabilities not found in most XAFS analysis packages.IFEFFIT is an interactive program and scriptable library for XAFS analysis and FEFF fitting. It combines the core algorithms of AUTOBK and FEFFIT with general data manipulation and interactive graphics into a single package. IFEFFIT is available as a command-line program that can be run interactively or in batch mode, and provides a library of functions usable from C, Fortran, and high-level scripting languages like Tcl, Perl, and Python. A graphical user interface (GUI) is demonstrated for rapid 'online' data analysis. IFEFFIT is freely available under an Open Source license, encouraging outside use, development, and contributions. The introduction highlights the importance of high-quality, easy-to-use programs for XAFS data analysis. Dimakis and Bunker's APEX program demonstrated the feasibility of such a program. IFEFFIT aims to provide robust EXAFS analysis procedures and a facility for users to write macros, scripts, or programs for repetitive tasks. It also emphasizes the need for form-based GUIs, predictability, and uniformity in analysis procedures. The command-line interface allows users to read, write, and manipulate data, including XAFS analysis procedures, Fourier transforms, and FEFF calculations. IFEFFIT supports data manipulation and plotting, and data is stored as one-dimensional arrays. It supports basic mathematical operations and has a simple command-line interface. The programmer's interface allows IFEFFIT to be used from Fortran or C programs, and also from high-level scripting languages. The IFEFFIT library provides seven basic functions for accessing the underlying "IFEFFIT session" and its data. The principle function, ifeffit(), executes IFEFFIT command strings as if they were typed at the command-line. G.I.FEFFIT is a graphical interface built using Python, providing forms for common analysis tasks like data reading, plotting, and XAFS analysis. It is still in development and lacks a complete form-based interface for FEFFIT-type fitting, but is a flexible program for simple data processing, plotting, background subtraction, and Fourier transforms. IFEFFIT is free software, distributed under an Open Source license. It is in an early stage of development, though most algorithms needed for XAFS analysis are supported. It lacks some advanced features like simultaneous fitting of multiple data sets and improved background refinement, but has many capabilities not found in most XAFS analysis packages.