Suggestions for xstring
The following packages have something in common with the package xstring. The packages are ordered in decreasing similarity.
- xesearch: A string finder for XeTeX
 - coolstr: String manipulation in LaTeX
 - metastr: Store and compose strings
 - string-diagrams: Create string diagrams with LaTeX and TikZ
 - formlett: Letters to multiple recipients
 - expex: Linguistic examples and glosses, with reference capabilities
 - binhex: Convert numbers into binary, octal and hexadecimal
 - trigonometry: Demonstration code for cos and sin in TeX macros
 - ean: Macros for making EAN barcodes
 - bagpipe: Support for typesetting bagpipe music
 - code128: Barcode macros for the Code 128 standard
 - cdlabeler: Take user text and typeset it to fit a CD label
 - cptex: Use different code pages for TeX input
 - c-pascal: Typeset Python, C and Pascal programs
 - dirtree: Display trees in the style of windows explorer
 - eijkhout: Victor Eijkhout's packages
 - lpform: Typesetting linear programming formulations and sets of equations
 - librarian: Tools to create bibliographies in TeX
 - lecturer: On-screen presentations for (almost) all formats
 - mathdots: Commands to produce dots in math that respect font size
 - occam: Strip unnecessary macros from a file
 - pmat: Typeset partitioned matrices
 - poster-mac: Make posters and banners with TeX
 - path: Typeset paths, making them breakable
 - rlepsf: Rewrite labels in EPS graphics
 - texchord: Typeset guitar-chord diagrams
 - upca: Print UPC-A barcodes
 - vrb: Verbatim macros in plain TeX
 - shade: Shade pieces of text
 - upzhkinsoku: Supplementary Chinese kinsoku for Unicode *pTeX
 - apnum: Arbitrary precision numbers implemented by TeX macros