CopyTrans HEIC for Windows - A plugin that lets you view HEIC photos on Windows and convert them to JPG by right-clicking.
digiKam - Professional Photo Management with the Power of Open Source
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
iMazing HEIC Converter - iMazing HEIC converter is a free Mac and PC app which converts photos from HEIC to JPEG or PNG.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Icaros - Icaros is a collection of lightweight, high quality, Windows Shell Extensions