It's quite likely that the mancala family of games are the oldest games of all. There are mancala game pits carved from stone that have been found in Africa that are estimated to be about 3,500 years old. This doesn't make them the oldest games found by archeology -- Senet and game boards from Ur are older -- but considering the nature of mancala there's good reason to suspect it's much older.
For one thing, the stone-cut pits are rather unusual. Someone went through a considerable amount of trouble 3,500 years ago to create a permanent game "board" by making those pits in stone. But mancala is normally played on wooden boards with carved out pits, and is also often simply played in the dirt, with holes scooped out of the ground. Neither of these play surfaces are durable, of course, and could have been used thousands of years ago without leaving any trace. (This is a good place to remember that archeology has unavoidable biases. We can only know about what circumstances allowed to be preserved. We know about "stone age" cultures largely because of their stone tools, but it's likely that most of their belongings were made of more perishable things like wood, skins and bone that aren't often preserved.)
Likewise, mancala is normally played with common items such as pebbles, seeds, sea shells or bits of grain instead of purpose-made game pieces such as Senat had. Again, these are less likely to be preserved, and even if preserved, probably wouldn't be recognized for what they were. After all, how does one know what a pile of pebbles was used for?
Mancala games are played throughout those parts of the world where people have lived the longest. While there are many variations, they all involve the very simple game mechanic of scooping up the pieces from a pit and "sowing' them in other pits to capture the contents of other pits. This mechanic is evocative of the tasks involved in ancient agriculture, and that, indeed may be its origin. We know from our own lives that play often mimics activities of real life.
Oh-Wah-Ree was an updating of the mancala game that was first published by 3M in 1962. Played under the standard rules, Oh-Wah-Ree is simply mancala played using a circular arrangement of pits instead of the traditional side-by-side rows. The primary innovation of Oh-Wah-Ree are rules for scaling the game to 3 or 4 players. This is so simply done, one has to wonder why traditional mancala is so solidly a two-player game. The name "Oh-Wah-Ree" is simply a phonetic spelling of "Awari," the name the game goes by in the West Indies and Guyana.
Mancala games, although of worldwide popularity, don't fare all that well among hobby gamers. As is common with traditional abstract games like backgammon, chess, go and morris, mancala seems to have limited appeal with adult hobby gamers, who prefer games with more explicit themes and clever game mechanics. Oh-Wah-Ree, like other traditional games, has very few rules and is easily taught and passed on generation to generation by an oral culture. Like those other games, however, simple rules does not mean the game is simplistic, and even a standard game can be challenging if played competitively.
Under the standard rules of Oh-Wah-Ree each player starts with the same number of stones in their pits. Each player in turn picks up the contents of one pit and sows them one-by-one in consecutive pits until they run out. If sowing a stone in the last pit causes that pit to have 2 or 3 stones on the opponent's side then the sowing player captures those stones and puts them aside. If the penultimate pit also has 2 or 3 stones then those are also captured, and so on until the series ends by having 4 or more, or 1 or none or reaches the sowing player's own territory.
The game ends when one player has no stones to play and the winner is the person with the most stones. It's not allowed to count the stones and the inability of people to tell at a glance the exact number of stones when there are 5 or more prevents the game from being a simple math exercise.
The sowing mechanic is a tactilely satisfying one, and the game is a good one for parents to play with children.
Oh-Wah-Ree has rules for some more complex variations based on more involved variants of mancala played in Africa, Asia and the Caribbean, but the standard game is fine for casual play.
Oh-Wah-Ree also has rules for 'Grand" Oh-Wah-Ree, where players capture pits as well as stones for another variation.
Oh-Wah-Ree is long out of print, but not that hard to find on eBay. Traditional mancala games are available everywhere and are easily fabricated. If you're on the beach a few minutes gathering sea shells and scooping out pits in the sand is all you need to get started.
Mancala, like chess, checkers, go, backgammon dominoes and cards should be part of any household's basic gaming library.