I like WebVOWL for visualizing the RDF ontology. Here's the pbprdf ontology displayed in it: http://www.visualdataweb.de/webvowl/#iri=https://raw.githubu...

A few years ago I put together a quick GUI in C# to make it easier to run SPARQL queries: https://github.com/andrewstellman/sparql-explorer

I haven't found an RDF editor or visual tool that I like. Some people like Topbraid Composer: https://www.topquadrant.com/tools/modeling-topbraid-composer... (commercial, closed source)