Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
iMazing HEIC Converter - iMazing HEIC converter is a free Mac and PC app which converts photos from HEIC to JPEG or PNG.
DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
QuickLook - Bring macOS “Quick Look” feature to Windows.