What is the nature of morality without God?

If there is no God, how should we live? What are the foundations and framework for morality? How do we determine what is right and wrong?
Personal conscience, intuition, social consensus, utilitarianism, .... ? How do we decide?
Individuals must decide. Communities must decide, on both social expectations and legal requirements.
To me, the lack of clarity on this issue is one of the intellectual and practical problems with atheism.
In contrast, Christianity provides a clear foundation for ethics and morality. That does not mean that it is therefore true; just that this is an appealing feature.
I recently realised there is more to this issue.

In Mere Christianity, C.S. Lewis considers the problem of morality. In his characteristic clarity he introduces the analogy of a fleet of ships traveling to a destination.
There are three practical issues relevant to a safe and successful journey:

How do you make sure each individual ship is seaworthy?
How do you stop the ships from colliding with each other?
How do you decide on the destination and the route to get there?

A brief summary of Lewis on this is here.

The corresponding moral questions are:
How do individuals decide on their private morality? i.e. what they think and do when alone.
How should individuals interact with each other in a way that is not harmful to one another?
What is our moral vision for society? How do we head in that direction?

Most discussions of ethics and morality, and the relevance or not of God, focus on this second question. However, I now realise that a compelling attraction of Jesus is the vision he offers of a just and loving society, and he claims to offer the power to make it happen. This is the Kingdom of God he talked so much about.

For me competing visions from atheism, materialism, Marxism, neoliberalism, religious nationalism, ... are impoverished.

Jesus does not just offer a foundation for morality but a compelling vision for a moral society.