ssss is an implementation of Shamir's secret sharing scheme for UNIX/linux
machines.

Citing from the Wikipedia article about Secret Sharing:

In cryptography, a secret sharing scheme is a method for distributing
a secret amongst a group of participants, each of which is allocated
a share of the secret. The secret can only be reconstructed when the
shares are combined together; individual shares are of no use on their
own.

More formally, in a secret sharing scheme there is one dealer and n
players. The dealer gives a secret to the players, but only when specific
conditions are fulfilled. The dealer accomplishes this by giving each
player a share in such a way that any group of t (for threshold) or
more players can together reconstruct the secret but no group of less
than t players can. Such a system is called a (t,n)-threshold scheme.

ssss does both: the generation of shares for a known secret and the
reconstruction of a secret using user provided shares.