PerfectCompress

PerfectCompress is yet another of those multi-archiver programs (for Windows) that supports the Usual Suspects of archiving formats like ZIP, and some more obscure ones, but also saw fit to introduce yet another new format of its own, UCA (ULTRA Compressed Archive, with ULTRA standing for ULTimate peRfect space sAver). Well, the author claims that it's not really a new format, since it's just a combination of existing formats: the files are compressed with PAQ, then compressed again with 7z, and a file is included automatically which indicates which version of PAQ to use to extract it (since different versions are incompatible with one another).

Links and References

 * Author's announcement and discussion
 * Download page