The free converter sites are full of ads and upload your files to who-knows-where. File Converter does it on your machine with tools already built into macOS. Pick a file and it offers the right targets: images to JPG/PNG/TIFF, audio to WAV/AIFF/M4A, documents to TXT/RTF/HTML. Nothing leaves your computer.
Drop in an image or audio file, or click Choose a file. File Converter reads it right here in your browser, figures out what it is, and shows you the formats it can save it as. Pick one, convert, then download the result. Nothing is uploaded - every byte stays on your machine.
Prefer a local copy? ↓ Download the macOS version
FileConverter.command.sips, audio uses afconvert, documents use textutil, all built into macOS. MP3 export is not available from the macOS audio encoder.