JPEG is where photographs live. Its compression is lossy - it throws away detail the eye is bad at noticing, and throws away a bit more every time you re-save - which buys huge size savings on photos and makes a mess of screenshots and text. There's no transparency in it at all.

Every conversion below runs in this page, on your own machine. Nothing is uploaded, there is no queue, and there is no account to make. Pick a target format, or just drop a JPG file above and choose afterwards.