Suggestions for spalign

The following packages have something in common with the package spalign. The packages are ordered in decreasing similarity.

Package gridset: Grid, a.k.a. in-register, setting
Package grid: Baseline-grid typesetting in LaTeX
Package returntogrid: Semi-automatic grid typesetting
Package eqnarray: More generalised equation arrays with numbering
Package cases: Numbered cases environment
Package subeqnarray: Equation array with sub numbering
Package amsthm: Typesetting theorems (AMS style)
Package keytheorems: An l3keys interface to amsthm
Package colophon: Provides commands for producing a colophon
Package writeongrid: Write on grid lines
Package autobreak: Simple line breaking of long formulae
Package thmtools: Extensions to theorem environments
Package kbordermatrix: LaTeX version of \bordermatrix
Package plain-grid: Four sets of macros for typesetting on a baseline grid
Package newproof: Make commands to define proofs
Package thmbox: Decorate theorem statements
Package shadethm: Theorem environments that are shaded
Package ntheorem: Enhanced theorem environment
Package eqnalign: Make eqnarray behave like align
Package delarray: Delimiters for arrays
Package systeme: Format systems of equations
Package nicematrix: Improve the typesetting of matrices and tabulars with PGF
Package theorem: Manipulate theorem environments
Package create-theorem: Initializing and configuring theorem-like environments, with multilingual support
Package upgreek: Upright Greek letters
Package theoremref: References with automatic theorem names
Package odesandpdes: Optimizing workflow involving odes and pdes
Package phfthm: Goodies for theorems and proofs
Package inkpaper: A mathematical paper template
Package simples-matrices: Define matrices by given list of values
Package easymat: A simple package for writing matrices