Russian firefly goes with Russian-English and English-Russian dictionaries, but without sound.
You need to have 3 files with dictionary: .dict.dz, .idx, .ifo
You can put them to dicts folder in internal memory or microSD card.
PDFReader is not such good as new one for i62HD without firefly, but I hope Booxtor makes new firmware soon.
You make own programs for Onyx, but it is not easy, because there is no documentation.
You can install chess, reversi, checkers and some more games.