An ISV (independent software vendor) makes and sells software products that run on one or more computer hardware or operating system platforms. The companies that make the platforms like Microsoft, IBM, Hewlett-Packard, Apple, and others encourage and lend support to ISVs, often with special "business partner" programs. In general, the more applications that run on a platform, the more value it offers to customers. Of course, platform manufacturers such as Microsoft and IBM make applications, too, but don't have the resources and, in many cases, the special knowledge required, to make them all. Think of all the programs that run on your Windows 2000 or Mac platform and you'll realize how many ISVs there are. Some ISVs focus on a particular operating system like IBM's small business AS/400 for which there are thousands of ISV applications. Other ISVs specialize in a particular application area, such as engineering, and develop software primarily for high-end Unix-based workstation platforms.
ISVs make and sell software that is added to platforms. Original equipment manufacturers (OEMs) use hardware platform components to build larger products. Value-added resellers (VARs) incorporate platform software into their own software product packages.