Once upon a time, there was a global, instantiatable “GlideFilter” object. It was a little ugly and unintuitive, but it technically worked; usually. Nowadays though, the GlideFilter object is a scoped-API object (also available to the global scope) that is not instantiatable, and which has… some problems.
ServiceNow is aware of these problems, but - although they continue to use GlideFilter in their scoped apps (such as for vulnerability grouping rules in the Vulnerability application, which have been broken by the use of GlideFilter as of London - PRB1329737) - they have refused to fix the issues (PRB605673).

“What problems”, you ask? - Read on, to find out, and to see the solution/free tool!