Given a directory with some server, this library / rule should identify what server it is and what version. Vendor, model, version range.

Two principles will work here:
1) Quick identification by server-specific attributes - ideally a file with the version, but also a file which changes with every version.

2) Identification by hashes of all files in the directory.

Both will be extensible. 1) will be implemented by classes specific for each server vendor/model/major version. 2) Will use shared code for identification and use data sets for recognizing matching/changed/missing files. Extensions and data sets are subject to externalization - can be carried in other addons.