Free PNG Optimizer is a lossless compression tool which can reduce the size of PNG files without affecting their image quality.
The program looks and feels very professional. There's a quality ribbon interface; you can add files, folders, folder trees or more in a second or two; there's great control over the output images, and it all feels very configurable.
And the results aren't bad, either. We tested the program with a sample of 50 PNG web graphics, grabbed from real web sites, and Free PNG Optimizer compressed them by an average of 32%. That's impressive for files which you'd expect to be already heavily optimized, and if they were on your website, could help make a real difference to its performance and your bandwidth use.
If there's a problem here, it's that Free PNG Optimizer has a lot of competition. PNGGauntlet, for instance, combines three PNG compression tools to produce even more effective results, and managed to shrink our test images by 42%. Other tools also compacted our test images by more than 40%.
The results these programs can produce will vary a great deal depending on the source graphics, though, so if PNGGauntlet and other compression tools haven't been effective for you then it's definitely worth giving Free PNG Optimizer a try.