SageMath 9.2 has been released on 24 October. The Linux and macOS binaries are available at https://www.sagemath.org/download.html.
Those for Windows should follow soon, as well as Docker images. SageMath 9.2 is also available online at https://cocalc.com.
Regarding calculus on manifolds, SageMath 9.2 introduces new features:
– orientation of manifolds and vector bundles
– dot_product(), cross_product() and norm() can be now be used for vector fields defined along a curve in a pseudo-Riemannian manifold
– action of a bundle connection on sections
– Greek letters (and more generally Unicode characters) are now allowed in index notation for tensors
– diff(f) can be used to get the exterior derivative of a differential form f
– various code improvements and bug fixes
See https://sagemanifolds.obspm.fr/changelog.html for details and examples.
SageMath is a free computer algebra system based on Python, with some differential geometry and tensor calculus capabilities See https://sagemanifolds.obspm.fr/examples.html for examples of use, in particular in the context of general relativity.