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.CLS file extension - ArcView geocoding classification
What is cls file? How to open cls files?
File type specification:
Geocoding is the process of assigning a location, usually in the form of coordinate values, to an address by comparing the descriptive location elements in the address to those present in the reference material.
ArcView's geocoding engine uses US Postal Service street abbreviation conventions. These conventions are controlled through classification files that standardize address component abbreviations.
The default software associated to open cls file:
ArcGIS for Desktop Basic (ArcView) 
Company or developer:
Esri
ArcGIS for Desktop Basic (formerly known as ArcView) is GIS (geographic information system) application used to visualizing, managing, creating, and analyzing geographic data.
ArcGIS for Desktop Basic is a part of the ArcGIS Desktop. ArcGIS for Desktop Basic supports creation of interactive maps, spatial analysis, GIS deployment, map viewing and navigation, map printing etc.
List of recommended software applications associated to the .cls file extension
Recommended software programs are sorted by OS platform (Windows, macOS, Linux, iOS, Android etc.)
and possible program actions that can be done with the file: like open cls file, edit cls file, convert cls file, view cls file, play cls file etc. (if exist software for corresponding action in File-Extensions.org's database).
Unspecified and all other actions for computer programs working with cls file - ArcView geocoding classification
Click on the software link for more information about ArcGIS for Desktop Basic (ArcView). ArcGIS for Desktop Basic (ArcView) uses cls file type for its internal purposes and/or also by different way than common edit or open file actions (eg. to install/execute/support an application itself, to store application or user data, configure program etc.).
