Ashton-Tate dBase was an early popular database management system for CP/M and MS-DOS. It was regarded as one of the killer applications for CP/M, and achieved good success. At the time of conception Ashton-Tate was a garage based company but quickly grew.

dBase Mac, originally developed by a small company named DigiCorp and then marketed by Ashton-Tate under the dBase name, was a unique and powerful database program for the Macintosh. It featured a sophisticated graphical user interface, a procedural programming language, and the ability to access data from other databases and spreadsheets. 1.00 was released in 1987.

Decision Pad, from Apian Software, is a decision support tool that uses a decision matrix approach. It also supports a three-dimensional decision matrix for group decisions, and can import/export data from Lotus 1-2-3 files. It competed against a similar tool called "Prism".

DECTalk was a text to speech system used in automated telephone, radio, and TV systems. It was notably used as an artificial voice by Stephen Hawking. Most DECTalk devices were standalone serial devices, however DEC did produce an ISA expansion card for the IBM PC that contained this functionality. This software is required to operate these ISA cards.

Back before MapQuest or Google Maps, people could own an entire USA road map on a CD-ROM. DeLorme Street Atlas was one of the most popular road mapping products. You can search for street names or by phone number and zoom in on local neighborhoods. enabled users to create customized maps. focused on road maps. Later it competed with Microsoft Expedia Streets and Rand-McNally Route Planner.

DeltaGraph, originally from DeltaPoint and later SSPS, was a powerful business and scientific statistical graphics package for the Apple Macintosh and Microsoft Windows. graphics-only packages like Excel.

DeluxePaint, from Electronic Arts, is a bitmap pixel graphics editor that was ported to DOS from the Amiga.

DeluxePaint Animation is a raster based animation program based on the DeluxePaint painting program. It features ease of use, powerful drawing functionality, and a playback utility. As a DOS program, it was limited to 640k and 320x200 resolution in 256 colors.

Deneba Canvas is a shape based drawing and illustration program for the PC and mac. Unlike other publishing programs of the time, Canvas combined the ability to use vector graphics and raster images. It could also function as a word processor.

Derive was a computer algebra and graphing system, developed as a successor to muMATH by Soft Warehouse, Inc. in Honolulu, Hawaii, now owned by Texas Instruments. Derive was implemented in muLISP, also by Soft Warehouse. The first release was in 1988 for DOS. It was discontinued on June 29, 2007 in favor of the TI-Nspire CAS. The last and final version is Derive 6.1 for Windows.

DeScribe is a word processor with some advanced features primarily for OS/2. Later, it was made available for Windows 3.1, 95, and NT.

Design It! 3D is an easy to use budget 3D modeling tool. It is suitable for creating home arrangement designs, and features a 3D preview that lets you "walk" through your creation.

DesignCAD is a low end, but well featured, drafting program. It was sometime a companion product to DesignCAD 3D.

DesignCAD 3D is a powerful, easy to use, and low cost DOS based CAD program that claimed to have all of the features of the more expensive CAD programs. It competed against low-cost CAD programs such as TurboCAD, Generic CADD, and Drafix. It was sometimes sold alongside DesignCAD 2D

DevTech's Deskman/2 is a set of desktop and system management tools for OS/2. It contains data compression tools, networking tools, performance monitoring tools, and desktop management tools.

DESQView, from Quarterdeck, was a DOS application multi-tasker and in later versions functioned as an X client for applications on remote UNIX systems. It competed against IBM Topview. The original DESQ was just a task switcher, but subsequent versions offered preemptive multitasking of well behaved DOS programs on real-mode 8088 PCs. It gained popularity when DESQView 386 added virtual x86 support. This enabled the ability to multi task many poorly behaved programs, and was often used on BBSes due to its excellent COM port handling. It was later overtaken by OS/2 and Windows.

Diagram-Master, from Decision Resources and later Ashton-Tate, is a graphics tool specifically geared toward making organization and Gantt charts. It can produce very high-quality presentation graphics using laser printers and plotters. Supports CGA, EGA, and the IBM Professional Display. This program was also bundled in the Master Graphics Presentation Pack.

Diagraph, from Computer Support Corporation, is a program that lets users assemble presentations, charts, and graphs from a very large library of predefined symbols.

Released in 1997 by DayBreak Software, Break A Day is a calendar that shows a different Dilbert comic every day. Includes a 16-bit Windows 3.1 version, 32-bit Windows 9x/NT version, and a Mac version.

Direct Access is an easy to use menuing program designed to simplify access to applications on systems with many programs loaded on the hard drive. It is customizable, includes screen blanking, and includes password protection and usage logging. Later versions also detect common programs already installed on the hard disk.

Disk Technician, from Prime Solutions Inc., is a hard disk utility and surface monitor. It contains an interleave adjuster and pattern tester similar to Spinrite. The Gold version also includes a defragmenter and disk-level virus protection.

This is a low-end spreadsheet program from Disk-Count software, a vendor notable for their budget software titles. "This program is designed for the first time user with the capability for more advanced users. A spreadsheet is ideal for calculating any set of numbers that you normally would do by hand. Some of the uses are for preparing home budgets, calculating financial payments, tracking car expenses, and creating statistical models."

DiskClone, from Quarterdeck, is a simple, professional, small, powerful, and easy to use hard disk cloning tool. It can copy a drive to another internal or external drive of different sizes. It can be used as a backup, or a migration tool to a new drive. It all fits on a single floppy disk. "Corporate" editions.

DiskDoubler is an automated file compression program for the Apple Macintosh. It does not compress the entire drive, but rather specified files. It automatically compresses and recompresses files as you use them.

Diskeeper is a professional disk defragmenting tool with versions for both 9x and NT. It includes features such as scheduling and background defragmentation.