4DOS

4DOS is a command-line interpreter by JP Software, designed to replace the default command interpreter codice_1 in Microsoft DOS and Windows. It was written by Rex C. Conn and Tom Rawson and first released in 1989. Compared to the default, it has a large number of enhancements.
4OS2 and 4NT are similar products that replace codice_2 in OS/2 and Windows NT respectively. 
Overview.
4DOS is most often used as a command-line replacement for the following operating systems:
Since Windows NT and Windows 2000 includes both codice_1 and codice_2, 4DOS and 4NT and derivatives can both be installed. 
Earlier versions of 4OS2 can be run under Windows NT, and OS/2 can run the two DOS and Windows NT shells, all three can be used on Windows NT-type machines and OS/2 multiple boot machines.
Among the many commands, statements and functions in 4DOS and lacking in MS-DOS/Windows 95/98 codice_1 are reading keyboard input and a simpler method of working with colors of screen and text.
The default file extension for 4DOS scripts is .btm.
A graphical version of 4DOS, 4OS2, and 4NT, called Take Command, was released with a feature set corresponding to version 4DOS 5.5, 4OS2, and 4NT 2.5 and updated after this. Development on this line stopped with the corresponding text mode versions. There was a graphical program Take Command/16, for Windows 3.1.
4OS2 is a similar replacement for IBM's OS/2 command interpreter. This was first released at the same time as 4DOS version 4, and has a similar feature set. Like 4DOS, this is released as open source. It appeared in the feature set of 2011's eComStation 2.10, in the freeware os2free project, and is included with ArcaOS.
4NT was first released as "4DOS for Windows NT" (versions 1.x, 2.x), but became 4NT until the restructure after version 8. The program is a recompilation of 4OS2, and continues to have features of OS/2's command processor (codice_2), such as running REXX scripts, and EXTPROC support. A corresponding "Take Command/32" exists for this, version 1 corresponding to 4NT 2.5. 4NT and Take Command/32 were released in both ANSI (Windows 9x) and Unicode (Windows NT) forms, with the ANSI version dropped at version 5.
A new Win32 program Tabbed Command Interface (TCI), was released at the time of 4NT version 7. This program allowed one to attach (thereby reducing screen clutter) and detach tabbed consoles to a single window. This program requires Windows XP or later.
A new version of Take Command extends the original Tabbed Command Interface, expanded with extra windows to allow input to be composed, to graphically navigate directories and files, and extra features. 4NT is bundled as Take Command Console. A light feature-reduced version of TCC is released as a free download.
JP Software then released:
This has been released from versions 9 to 12.1, corresponding to the underlying 4NT/TCC version.
Features.
4DOS features a number of enhancements compared to codice_1:
History and current status.
Originally distributed as shareware, 4DOS has been later released as unsupported freeware. Currently, the source code is available under a modified MIT License but it "may not be used in any commercial product without written permission from Rex C. Conn" and "may not be compiled for use on any operating system other than FreeDOS" - so does not qualify as open source as defined by Open Source Initiative.
The last update by JP Software was version 7.50.130, released in August 2004. During its 15-year history, 4DOS underwent numerous updates; here are a few of the most significant.
NDOS.
Some versions of the Norton Utilities for DOS included modified copies of 4DOS called NDOS. The last version of NDOS was bundled with Norton Utilities 8, and corresponded to 4DOS 4.03.