ShanaEncoder is an audio and video encoding program based on FFmpeg designed for beginners and professionals.
You can open most file formats by going to File, Open, or you can drag and drop it right into the program's main window. You can then choose from numerous options and preferences. On the right, you will find converting settings you can access quickly. Many choices are broken down into categories, including Convert, Copy, Apple, Cowon, HTC, Invio, Iriver, LG, Mando, MobilePhone, Samsung, Sony, and YujinPNP. We didn't count, but there must be 50 possible formats to convert.
Once you've made your choice, select start; we were able to convert an 18MB MP4 video to a 13MB AVI in under a minute.
Free encoders or converters exist but can be hit or miss. ShanaEncoder can convert to just about any format for free. While it does give you the generic format to which you're converting (Apple, HTC), it should also let you know what you're converting to (AVI, MPEG, MP4, etc.).