The Business Operating System, one of a number of operating systems referred to as BOS, was an early cross-platform operating system originally produced for Z80 based machines, but later ported to most microcomputers of the 1980s. BOS National intended BOS to protect customers from changes in computer platforms, allowing BOS programs to be run on any machine running BOS. Its command line nature doomed it when GUI operating systems took over the market after the introduction of the Apple Macintosh.

BOS was designed to run programs written in p-code which would then be interpreted as they ran. At the time this was considered to be a major problem, as interpreters generally run slower than compiled programs. The increasing performance of computer hardware has generally made this a non-issue today, and the concept of p-code has been widely re-introduced in languages such as Java, where it is referred to as a virtual machine.

A range of software was available under BOS, including BOS/Finder (a database manager), BOS/Planner (spreadsheet), BOS/Writer (word processor), BOS/AutoClerk (report generator), and a suite of accounting software including BOS/Accounts Receivable, BOS/Accounts Payable, BOS/General Ledger, BOS/Inventory Control, BOS/Invoicing, BOS/Sales Order Processing. A number of languages were also available, but BOS/MicroCOBOL was the most common.