ACodec is an Open Source GUI encoder and decoder for Windows and Linux that utilizes various algorithms and charsets.
The interface is simple enough to use but packs a punch with over 30 different algorithms to choose from and numerous charsets from Big 5 to Windows ISO 2022 jp. The interface is broken into sections, one for input and one for output, so that you can enter in manual text for encoding/decoding. There is also the option to process an entire file - perfect for decreasing its size for a smaller footprint while storing.
ACodec is a straightforward app with an easy-to-navigate interface that makes it usable for anyone wanting to convert one format to another or reduce size for storing regardless of experience.