Everybody, who is interested in chess, uses databases to collect games. Probably only private games of yourself and your chess club, but if the interest goes deeper you will collect games of grandmasters and much more. Here I will describe tools and frontends to work with your game collections.
The standard to exchange game collections is the Portable Game Notation standard PGN.
A commandline client to achive a lot of tasks on .pgn files is pgn-exract. This tool is a commandline client to find duplicates, ECO classify your games, do spell checking, match for material and much more.
Features: calculate ELO ratings
Calculates bayesian ELO ratings out of .pgn files. It is a commandline tool, that does all the rating claculation in a sort of calculating shell. It ist scriptable with .cui files. Different mathematical calculating options.
Arena for Windows with wine-emulator
Features: analyse, FEN, EPD, multiple engines