As per request of WhiteRabbit, I'm working on modding Hyperballoid. They use a file format that's similar to Deep Voyage's, except with more spacing for filenames.
Initial findings...:
This file format is little endian. The format's identification string is the first four bytes, "DATF". It's followed by an encryption tag, 0A 00 00 00 for unencrypted, 0B 00 00 00 for encrypted. Next is a file count tag of four bytes (presumed; unverified). After that, it immediately list included files. Each file header consists of a file path, which takes up a lot of bytes (100, to be exact, but I'm not sure if all of that is used for the filename, or some of it is reserved for other things). Then comes data start location, and data length. After that are 20 bytes, filled with zeros. And then a new tag starts.
I found that they accidentally packed their DAT maker into some of the archives. Unfortunately, none of those archives were left decrypted.
The encryption scheme is interesting. It uses standard XOR encryption, except that the keys are different for even and odd original bytes (that is, if the original byte was an even decimal number, the key is 0x42; if the original byte was an odd decimal number, the key is 0xC3. This does not mean that the bytes are decrypted alternately; it only applies to what the byte was before).