To make the licensing part clear, SPLinT is GPL v.~3:

% Copyright 2012-2020, Alexander Shibakov
% This file is part of SPLinT
%
% SPLinT is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% SPLinT is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with SPLinT.  If not, see <http://www.gnu.org/licenses/>.

SPLinT is a \TeX\ package for building parsers and scanners in
\TeX. Bison and Flex are used to create the tables that drive the
automata programmed as \TeX\ macros (thus, after the parser/scanner
has been completed it can be used in plain \TeX, without invoking any
outside software). The documentation included with the package has a
detailed description of the features of the produced parsers and
scanners. To get started, run `make' to create a manual (which can be
found as cweb/splint.pdf in the cweb/ directory) and take a look at the 
`examples' directory. Here is a short
description of the various files included in the collection.

Files:

cweb/* - executables and documentation:
    bs.w - Bison Sourcer(er): table code core for bison
    fk.w - Flex Kit(ten): table code core for flex
    common.w - common code for table generators
    bo.w - parser for the bison grammar
    lo.w - lexer for the bison grammar
    fo.w - parser for the flex grammar
    so.w - lexer for the flex grammar
    np.w - scanner and parser for token names
    ssffo.w - lexer for state grabbing
    mkeparser.w - parser output `driver'
    mkscanner.w - lexer output `driver'
    splint.w - documentation
    philosophy.w - rants
    checklists.w - checklists to follow when modifying SPLinT

tex/* - \TeX\ macros
    yy*.sty, yx*.sty, flex.sty - automata machinery
    trt1.sty - `\TeX\ runtime': temporary register definitions
    xarithm.sty - expandable arithmetic for parsing macros
    grabstates.sty - macros for state grabbing
    *tokenset.sty - token typesetting definitions
    gindex.sty -generic indexing macros 
    dcols.sty - multiple column output
    noweb.sty - noweb style references (local within a page)
    limbo.sty - limbo section macros
    frontmatter.sty - macros to typeset the cover page 

examples/* - various examples:
    count - an example of robust token counting macros.
    expression - a simple expression parser built with the package.
    ld - a typesetting parser for the \GNU\ linker, ld, with a very
        detailed implementation manual.
    symbols - a demonstration of the features of the bison and flex
        parsers included in the package.
    types - expandable arithmetic (e.g. addition and subtraction 
        macros that can be used inside \edef), tree data structure;
        incomplete and slow, merely a proof of concept; only 
        standard plain \TeX\ is used
    xxpression - an extended version of the `expression' 
        example above, with a demonstration of symbolic name 
        mechanism setup.

scripts/* - helper (perl, for now) scripts to aid in pre- and
    post-processing of various files

makefile.inc - common definitions
makefile.loc - placeholder file for local make rules
COPYING - license information
INSTALL - cursory instalation notes
README - this file
TODO - plans for future development
VERSION - the current version

The most recent version of this software can be downloaded at

    math.tntech.edu/alex/splint.tar.bz2