The Java ASN.1 Toolkit is a simple library for efficiently encode and decode ASN.1 specification using the most usefull encoding format like DER/PER/CER or DER.
File2QR is an Android app that let you encode any small file on the filesystem to a QR code. Conversely, you can decode the encoded file from the generated QR, with mobile's camera. File2QR is built on ZXing library.
YEnc is a Java decoder for the yEnc format. Although a sample app is provided to decode files, JyEnc was designed as a library to be used by applications needing to use yEnc encoded data.