There are very few truly uncontacted peoples left in the world -- that is, people who have never been colonized or settled or had their mineral rights exploited, who know virtually nothing of the outside world, and about whom the outside world knows virtually nothing. One of these communities live on North Sentinel island, at the tip of the Andaman archipelago between India and Malaysia to the east. Protected by jagged reefs, rough seas and a reputation for shooting outsiders with arrows, there have been relatively few serious attempts to contact the Sentinalese. Those that have been made have failed; even gifts and peaceful offerings left onshore by anthropologists and Indian government officials have been answered with a hail of arrows. When one such landing party actually made it to shore, the islanders simply vanished, seeming to melt into the jungle.
Since the late 90s, the official policy of the Indian government has been to leave the Sentinalese alone. Still, that hasn't stopped accidental run-ins from occurring; back in 2006, a boat carrying two fisherman accidentally drifted into the shallows of North Sentinel, and the fishermen were killed. When a helicopter was dispatched to retrieve the bodies from the beach, the islanders chased it away with arrows.
Here's what we know:
There are between 50 and 200 of them.
They don't have writing.
They don't know how to make fire; observations made by landing parties in deserted villages have concluded that the Sentinelese wait for lightning strikes, then keep the resulting embers burning as long as they can.
We know nothing of their language.
Videos exist of the Sentinelese, taken by anthropologists from distant vantages. This one consists mostly of footage from the 70s, and features a gift of coconuts being made to the islanders, and the islanders' response -- arrows fired at the anthropologists' boat, and a great deal of rude dancing and genital-waggling aimed in their direction.
Another isolated Andamanese tribe, the Jarawa, have somewhat recently decided to stop murdering those who attempt to contact them, and in a startling about-face, now seem to love frolicking with the outsiders who come to their beaches to study them.
I, for one, hope the North Sentinelese remain "uncontacted" and more or less unknown for as long as possible.