If imitation is the sincerest form of flattery, then the computer industry has always fallen all over itself to flatter itself.
The MITS Altair had been shipping for only a few months when its first competitor appeared on the scene. A company by the name of IMS Associates introduced (in 1975) a machine that was very much like the Altair 8800 but that corrected many of the flaws that were a part of that initial effort.
The IMSAI 8080, pictured here from one of the company's early advertisements, was functionally the same as the Altair 8800 but with a much beefier power supply and more slots. Significantly, the IMSAI 8080 was bus compatible with the Altair. The fact that IMS chose to emulate the Altair bus helped define it as an early "industry standard." The fact that this standard existed led to an aftermarket industry that was free to create products for a wider market and thus led to other manufacturers who were more apt to adopt this bus for their computer entries.
By the end of 1996 computer makers such as MITS, IMSAI, Polymorphic, SOL and others are building and selling Altair bus computers (now called the S-100 bus after the number of pins in its connection). There are still more companies producing add-in boards and peripherals.
The Intel 8080 and the S-100 bus weren't the only game in town, however. In 1976 MOS Technology introduced the 6502 microprocessor. Because this new chip was considerably cheaper then Intel's 8080 several people decided to use the 6502 instead. Amongst these were two Steve's, Jobs and Wozniak.
The Apple I, pictured here in a 1977 Byte Shop ad was created in 1976 in Steve Wozniak's garage workshop. The computer, like the Altair before it, had no keyboard and no display, but it was significant for several reasons. First, it had built in software so that it could do things "out of the box" (actually, the apple I was usually a kit, so out of the box and once built). Second, it had a built in keyboard interface. You had to buy or build the keyboard separately, but it could be attached to the Apple with relative ease. Third, it had a video subsystem. This allowed the Apple to be connected to a video device (typically a TV set) for output.
Apple wasn't the first to include all of these things in their computers, but they were the first to do it well.