The algorithms provided with Pline Weeder range from the very simple to the very complex and fall into three groups.
The simple algorithms work perfectly well and have the advantages of being easy to understand and giving easily predictable results. They have the disadvantage of not discerning significant features well.
Two of the algorithms were originally developed by the US Geological Survey and are therefore public domain. They are effective aglorithms and have been in wide use for decades.
The most complex and effective algorithms are proprietary to Beowolf Technologies. They were developed specifically for use with Pline Weeder. Though they could be readily adapted for use in other applications, it would be illegal to do so without first obtaining a license from Beowolf.