Breadbox Office — DOS software, but has been successfully tested with Windows 3.x, Windows 95/98/98 SE/ME, Windows NT 4.0, Windows 2000 and the 32-bit versions of Windows XP, Windows Vista and Windows 7.
Microsoft Office - Note that while Microsoft makes both a Windows and Mac version of Office, the Windows only version is named just Microsoft Office and has a slightly different feature set then the Mac version, which is named "Microsoft Office for Mac". While both are part of the MS Office family, they are separate programs, as the Mac version is not simply a port of the Windows version. (see Office suites for Mac OS X only section below).
Microsoft Works —Discontinued in 2009 and replaced by Microsoft Office 2010 Starter Edition.
OmegaOffice HD from SSuite Office - Created for full HD and large widescreen displays including 4K and 8K monitors. Runs on all Windows systems. 
Breadbox Office — A word processor, spreadsheet, address book and drawing program. It is part of a broader software package called Breadbox Ensemble which also includes programs such as email, web-browser and html editor. Breadbox Ensemble runs under the GEOS (16-bit operating system) and effectively requires a version of DOS to be installed on the host system.
Corel WordPerfect for DOS - A word processor, spreadsheet, and presentation software from Corel (containing WordPerfect 6.2, Quattro Pro 5.6, Presentations 2.1, and Shell 4.0c).
NeoOffice — NeoOffice is a Mac-specific open-source software development project dedicated to integrating OpenOffice.org with native features of OS X, in addition to an aesthetic and design language suited to said operating system. While the source code is available for free, developers charge for the binary version of this application.
Siag Office — a free office suite for Unix systems. Primarily written by programmer Ulric Erikkson, with contributions from other authors. Includes a word processor, a spreadsheet, and an animation program.
ContactOffice - an AJAX-based online office suite. The suite includes personal and shared Calendar, Document, Messaging, Contact, Wiki,... tools. Available free and as an enterprise service.
Google Docs — an AJAX-based online office suite from Google, Inc. The suite includes a word processor, a spreadsheet program, and a presentation editor. Available free and as an enterprise service.
ONLYOFFICE Personal, an online office suite, combines text, spreadsheet and presentation editors.
Windows Live Office - an online office suite from Microsoft which is based on Windows Live SkyDrive. It includes a word processor, a spreadsheet, a presentation application and a notetaking program. Allow users to create, edit, save and share documents.
Zoho Office Suite — a free online office suite from Zoho Corporation. Includes a word processor, spreadsheet, presentations, and collaboration groupware.
iWork for iCloud - A free-to-use but somewhat feature limited online version of Apple's iWorks office suite, that's accessible using both Mac and PC web browsers. It is currently still in beta.
ONLYOFFICE - an online office suite integrated with document and project management toolset and CRM system. It includes word processor, spreadsheet and presentation program written in HTML5 using Canvas.
ShareOffice — a Web-based office suite from ShareMethods. This suite utilizes separate word processing, spreadsheet, and presentation applications from other vendors. It is distributed through Salesforce.com's AppExchange program.
Simdesk — an online office suite from Simdesk Technologies, Inc. This suite offers partial compatibility with the Microsoft Office file formats (Word, Excel, and Powerpoint). With a monthly subscription to Simdesk Services (costing $3.50 – $20 per month), one is allowed to install the application anywhere. (not available any longer)
ThinkFree Office — an office suite written in Java, from ThinkFree, Inc. It includes a word processor (Write), a spreadsheet (Calc), and a presentation program (Show). For Microsoft Windows, Linux, and Mac OS X.
Comparison of general and technical information
AppleWorks (previously known as "ClarisWorks") — an early Mac Office suite. It has morphed and branched into AppleWorks and GoBe Productive. When the original developers split up, ClarisWorks continued as AppleWorks after being bought by Apple, and GoBeProductive was redeveloped from the ground up using ideas from the original. Apple discontinued this suite after the release of iWork '08 in August 2007.
Lotus Symphony — Following the popularity of office suites made by competitors, the makers of the wildly popular Lotus 123, tried their hand at a suite for DOS. (Name resurrected by IBM in September 2007 as IBM Lotus Symphony)
Lotus Jazz — Mac sister product to Lotus Symphony.
Open Access — Integrated software by Software Products International (SPI).