Source: Wikipedia Star Fleet Universe
available under the CC-BY-SA License.
The Star Fleet Universe (SFU) is the variant of the Star Trek fictional universe detailed in the series of Star Fleet Battles games (board-, card-, and role-playing) from Amarillo Design Bureau Inc. and used as reference for the Starfleet Command series of computer games. Its source material stems from the original and animated series of Star Trek as well as from other "fan" sources, such as The Star Trek Star Fleet Technical Manual. In addition, it also includes a substantial number of new races and technologies, such as the Hydran Kingdom, the Inter-Stellar Concordium and the Andromedans.
Star Fleet Battles was based on the Star Trek universe as of 1979  and includes elements of Star Trek: The Original Series and Star Trek: The Animated Series. Federation elements were heavily based on concepts from The Star Trek Star Fleet Technical Manual. Unlike the mainstream Star Trek universe, Star Fleet Battles seems to consider some, but not all of The Animated Series, as being a canon material source, thus leading to the inclusion of aliens such as the Kzinti, which had originally been created for a non-Trek story series.
Since the first publication of the game, Star Fleet Battles and the Star Trek universe have diverged considerably as the authors of the game and those of the films and television series have basically ignored each other. The resulting divergent world of Star Fleet Battles is known as the "Star Fleet Universe".
Games set in this universe include the tactical board wargames Star Fleet Battles, Federation Commander and Star Fleet Armada (a Star Fleet Universe adaptation of Majestic 12 Games' Starmada engine); the strategic wargame Federation and Empire; the card game Star Fleet Battle Force; and the role-playing game Prime Directive in editions for the GURPS, D20 and D20 Modern game systems. Also, ADB produces Captain's Log, a non-periodical journal published roughly semi-annually with additional SFU background material, starship information and reports from various game events and tournaments.
Star Fleet Universe products outline an extensive history that serve as the backdrop of the games. The usual chronology uses an Earth-based calendar (June, August, 365 days, etc.), with dates given in "Y-years". These are written as (for instance) Y168, or August Y168, and are dated to the year Earth first made contact with the Vulcans. A direct conversion to familiar Anno Domini dating is (purposefully) not given, however the Federation and Empire rules state that Y0 should be somewhere between AD 2020 and AD 2090, the Federation Commander rules arbitrarily set it as AD 2400 (referred to in-universe as the Valkenburg Chronology) and consistently use 'AD' dates derived from that rather than use 'Y-year' nomenclature, while an option setting the date at 2063 (in line with the year of First Contact set in other Star Trek settings) is known as the Amin-Audeh Chronology. In all cases, it is stated that the actual date cannot be precisely known.
As this chronology was created completely separately of anything done for Star Trek after the Original Series (which at the time also avoided any hard date for when it happened), it cannot (and should not) be reconciled directly with current Star Trek canon. As an example of the incompatibilities arising from the separate evolution of the two visions of Star Trek history, the SFU defines the "five year mission" of the original Star Trek series as being from Y155 to Y160, which by Paramount's chronology would put Y0 at AD 2108; while if one accepts the definition of Y0, it should be the year of the movie Star Trek: First Contact, AD 2063.
While the time periods recorded in the Alpha Octant, Small Magellanic Cloud and Triangulum Galaxy are only loosely arranged into particular eras, the history of the Omega Octant is broken down into 'Cycles', as recorded by the Chlorophon race (who act as the de facto fictional historians of the Octant). Such Cycles cover the defining events of each period, such as the Pax Mæsra (the period of the Mæsron Alliance's furthest extent in power and influence) and the Invasions (when the Andromedans and Souldra sought to conquer the Omega races).