UNIX is one of the few operating system that supports and can be run on a non-deterministic Turing Machine and use its full potential. Below is part of a C code solving 3-coloring (whether a graph can be colored in 3 colors) in non-deterministic polynomial time.

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int n, m, G[N][N], color[N];

int main() {
    scanf(" %d %d", &n, &m);
    for (int i = 0, u, v; i < m; i++) {
        scanf(" %d %d", &u, &v);
        G[u][v] = G[v][u] = 1;
    }
    for (int u = 1; u <= n; u++) {
        int ok[3] = {1, 1, 1};
        for (int v = 1; v < u; v++) {
            if (G[u][v]) {
                ok[color[v]] = 0;
            }
        }
        /* I will try the first color, my children try other options */
        color[u] = -1;
        for (int c = 0; c <= 2; c++) {
            if (!ok[c]) {
                continue;
            }
            if (color[u] == -1) {
                color[u] = c;
                if (u <= 2 || u == n) {
                    /* optimization */
                    break;
                }
            } else {
                /* branching, or some call this guessing */
                if (fork() == 0) {
                    /* I am the child */
                    color[u] = c;
                    break;
                }
            }
        }
        if (color[u] == -1) {
            /* we're on a rejecting branch */
            wait_or_fail();
        }
    }
    printf("SUCCESS: ");
    for (int u = 1; u <= n; u++) {
        printf("%d ", color[u]);
    }
    printf("\n");
    exit(SOLVED);
}

Although you are able to compile and run this on current x86 Linux machines, it is not recommended–the effects are pretty similar to the well-known :(){:|:&;}. Full source code is on my gist.