AFAIK, the leading alternative Critical Chain Method, which is no simpler to calculate, and I'm not sure that I would really advance it as a full altnerative - it is a different way of managing the critical path.
From memory, CCM perceives slack as a project level entity, rather than as an attribute of a work package - all slack is tracked at the end, and any work product that runs over can draw from project slack. This leads to teams being more honest about their pessimistic estimates.
I don't think it is really possible to have an alternative to CP; that would be like having an alternative to prime factorization, or an alternative to mass or density. All projects have a critical path whether you calculate or not. Some project managers many not use the CP to manage the project, but it is there, controlling the probability that the project will run over.
Microsoft project will automatically calculate Critical Path - I think it would be very helpful if other answers could reference the ability of other software packages to automatically calculate CP.