X00 was a popular DOS-based FOSSIL

FOSSIL

FOSSIL is a standard protocol for allowing serial communication for telecommunications programs under the DOS operating system. FOSSIL is an acronym for Fido Opus SEAdog Standard Interface Layer. Fido refers to FidoBBS, Opus refers to Opus-CBCS BBS, and SEAdog refers to a Fidonet compatible mailer...

 driver

Device driver

In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....

 which was commonly used in the mid 1980s to the late 1990s and is even still used today. FOSSIL drivers were mainly used to run BBS

Bulletin board system

A Bulletin Board System, or BBS, is a computer system running software that allows users to connect and log in to the system using a terminal program. Once logged in, a user can perform functions such as uploading and downloading software and data, reading news and bulletins, and exchanging...

 software under MS-DOS

MS-DOS

MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...

. X00 can also be run under Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

, or even Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

 and DOSEMU

DOSEMU

DOSEMU, alternatively rendered dosemu, is a compatibility layer software package that enables MS-DOS systems, DOS clones such as FreeDOS, and DOS software to run under Linux on x86-based PCs ....

 environments, to allow FOSSIL-aware MS-DOS based applications to function.

X00 was developed by Raymond L. Gwinn from 1989 until 1993. The final release version was version 1.50, with a later beta version 1.53 which added support for baud rates above 38400. X00 is free for non-commercial usage. X00 included many enhancements to the FTC FOSSIL revision 5 specifications, which were later used in other FOSSIL drivers such as ADF and NetFoss

NetFoss

NetFoss is a popular Network FOSSIL driver for Windows.A FOSSIL is a serial communications layer to allow DOS based software to talk to modems without dealing with hardware I/O and interrupts....

.

Gwinn moved on to develop a replacement serial port driver for OS/2

OS/2

OS/2 is a computer operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively. The name stands for "Operating System/2," because it was introduced as part of the same generation change release as IBM's "Personal System/2 " line of second-generation personal...

 called SIO

SIO (software)

SIO is a serial port driver package for OS/2 written by Raymond L. Gwinn. It is designed to not only improve performance over OS/2's default serial drivers, but also improve compatibility. SIO contains a virtualized FOSSIL driver that can be loaded to provide FOSSIL support to DOS based...

. SIO contained a virtualized FOSSIL (VX00) that could be loaded if applications needed FOSSIL support.