GIF is thirty-eight years old and refuses to die, because it animates and everything opens it. The cost is its palette: 256 colours per frame, so photographs come out visibly banded. Transparency is on-or-off per pixel, with no partial opacity.
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 GIF file above and choose afterwards.