SAN FRANCISCO — One after another, like moths to a flame, technology companies have been seduced into entering the market for tablets. Apple made it look so irresistible, with 29 million eager and sometimes fanatical consumers snapping up an iPad in the device’s first 15 months.

But neither Samsung nor Motorola nor Acer could beg or borrow any of Apple’s magic. Research in Motion, the maker of the BlackBerry, said it shipped only 200,000 of its PlayBooks in three months — about what Apple sells in three days. Hewlett-Packard, which flopped this summer with the TouchPad, was the latest to get burned.

Now comes a final competitor, the best-placed challenger of all: Amazon.com. The retailer is on the verge of introducing its own tablet, analysts predict, a souped-up color version of its Kindle e-reader that will undercut the iPad in price and aim to steal away a couple of million in unit sales by Christmas.

A competition between Amazon and Apple tablets will be a battle that pits the company that created the first popular e-reader (and set off a still-unfolding revolution in how books are consumed) against the company that created the first popular tablet (and set off a revolution in progress about how entertainment and other media are consumed).