• xparse, which provides a high-level interface for declaring document commands
• xfp, an expandable IEEE 754 FPU for LaTeX
• l3keys2e, which makes the facilities of the kernel module l3keys available for use by LaTeX 2e packages
• xtemplate, which provides a means of defining generic functions using a key-value syntax
• xfrac, which provides flexible split-level fractions

See also l3kernel l3experimental.

The author is The LaTeX Team. The package is Copyright © 1998-2011, 2015-2018 The LaTeX project.