Dark (full name 'Dark Archon') is a concatenation of famous BWT Archon3 with my DC implementation. Some info about Archon sorting techique can be read here: Archon3 final structre.
Today dark has special 'lite' version of Archon BWT, designed for simplicity and working stability.
Enc/dec speed is mainly symmetric. No filters at present time.
Fragmentation and Solid compression features are supported.
I don't say Dark is the best compressor ever known. No, it's far from be the best... But it's very good, it has an amazing speed. Moreover, I can definitely say the speed will not be lower when I'll gain compression ratio.
Ziff-Lempel (LZ): Texts are definitely belong to Dark territory. The main battlefiled here is binary data. Dark is faster (especially after v0.35b) but the compression is worser. Advanced fragmentation techinque here helps a lot, but it's not enough to gain same ratios.... LZ decoding is much faster.
Prediction by Partial Matching (PPM): Compression of Dark is mainly worser, but speed is better. Check it yourself ;0 Decoding speed of PPM is also symmetric, so it can't be used for distributives.
Burrows-Wheeler Transform (BWT): YBS,SBC,GRZIPII,UHBC - the deserved competitors. The real one is GrZipII, imho because of it's speed. It uses not less then 7N for compression and it's maximum block size is 8Mb (compartively to Dark: 5N, no block limit). It's speed is similar on texts and significantly worser on binaries.