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Apultra is actually a very old new packer at heart. Those of you who used executable compressors for 16-bit MS-DOS programs may remember aPACK by Ibsen Software, which was one of the best executable packers at the time. The compression format underlying aPACK is a fairly well tuned variation of LZ77/LZSS with rep-offsets, a sort of LZX-lite. aPACK became the basis for universal compression library ApLib, still available from Ibsen Software. It offered a decent compression ratio (worse than Exomizer but better than most other pure LZ77/LZSS compressors). It also had a fairly good balance between the compression ratio and decompression rate, so decompressors were ported onto many old systems and used, for example, in all ZX Spectrum games based on La Churrera engine.

The only bad thing about it was the fact that ApLib is freeware, but with closed source. The compressor was not updated for a fairly long while and the competition was gradually catching up.

It was recognized during the last few years that the format used by ApLib is not exploited by the official compressor fully. A series of compressors with better ratios than the official compressor were produced by enthusiasts. Notably, CAP by Sven-Åke Dahl got so good that it edged to just 1-2% behind Exomizer. This is particularly impressive because much simpler format of ApLib allows decompression at about twice the speed compared to Exomizer. Another very recent compressor OAPACK by Eugene Larchenko implemented a brute-force truly optimal compression into ApLib format, albeit at the expense of significant memory and speed requirements.

Apultra written by Emmanuel Marty is a pragmatic compromize offering nearly optimal compression into ApLib format at very competitive speed. It is an open source software with the zlib licence, written in pure C, which has about the same compression ratio as CAP (i.e. about 0.5% behind the truly optimum compression and about 1.5% behind Exomizer). It also provides a number of other useful features, such as the support for backward compression and the work with external dictionary files.

Apultra also comes with a number of new highly optimized decompressors. John Brandwood contributed a very efficient 6502 decompressor. Dan Weiss contributed an ARM7 decompressor. Emmanuel Marty implemented support for 8088 and x86. I contributed new size- and speed-optimized decompressors for Z80 - the size-optimized one is only 139 bytes long and the speed-optimized one is almost 20% faster than the previously fastest decompressor. Backward decompressors, at least on Z80, are even smaller/faster.

Basically, on 8-bit platforms it is a good option for when you need a reasonably good ratio, without having to sacrifice too much speed. On 16/32-bit oldschool platforms it is probably a good choice for when reasonably fast decompression is needed. Give it a try, it may surprise you.