Of course, if you want to convert a Base64 data to pretty much any type of file, you can just use the online tool at http://www.extramaster.net/tools/fromBase64/.
But on the off-chance that you are naturally suspicious of anything that anyone makes, here's a simple Base64 to PNG Windows application that can convert from Base64 to PNG offline and without internet.
So, without further adieu,
Download:http://static.extramaster.net/Base64 to PNG.exe
MD5: 991EFE1DD11EE004A218EDCDD0B523DC
SHA-256: E3E49B60989DDDEA2649DC7880E583475E931CB0F40A06A7EEFBC7085B92756C
https://www.virustotal.com/en/file/e3e49b60989dddea2649dc7880e583475e931cb0f40a06a7eefbc7085b92756c/analysis/1407166729//