Not free ($25), but worth mentioning because Cherry Audio makes modern plugins that run perfectly and sound incredible. Their or Mercury-4 are insane. But if you want exactly the Pro-53 experience, the CA-1200 (a Juno/Prophet hybrid) is often on sale for $9.
A part of the V Collection, offering high compatibility with modern systems. Native Instruments Super 8 Often suggested by Native Instruments as a contemporary alternative for vintage synth sounds. Native Instruments Security Warning native instruments pro 53 vst free download work