The X Series is a renowned franchise of computer games developed by the company Egosoft and currently consists of 8 distinct titles. The core gameplay is a deep mixture of space flight simulation, intense combat, and economic strategy, heavily reminiscent of classic games like Elite or Privateer. However, the economy in this universe behaves in an incredibly dynamic way—prices are determined realistically by supply and demand. Players have the total freedom to operate as a pirate or a merchant. Over time, you can even construct your very own vast empire consisting of spacecraft, space stations, and production factories.
Control and navigation are managed via keyboard and mouse or a joystick setup. The spacecraft can be freely accelerated, decelerated, and rotated across three distinct axes in open space.
Starting with X², the games feature a powerful built-in script engine and a versatile script editor. Over the course of time, dedicated fans have developed highly interesting and incredibly helpful scripts, which Egosoft officially compiles and offers as free downloads in their bonus packs.

Released in 1999, "X: Beyond the Frontier" introduces the background story of how the player, stepping into the role of test pilot Kyle William Brennan, ends up stranded in a remote sector of deep space due to a malfunction in a newly developed jump drive — the X-Universe. In his persistent efforts to discover a way back to Earth, he encounters five distinct alien species and gathers allies and vital resources for the inevitable battle against the hostile Xenon race.
In this first installment, the X-Universe consists of 54 space sectors, which are all interconnected through a network of ancient jumpgates.

One year later, "X-Tension" was released. Although it requires the original X:BtF CD to run, it is a completely separate, standalone game. Since 2001, both titles have been bundled and sold together as "X-Gold". In this expansion, a fixed main plot was replaced by randomized minor missions and dynamic contracts. The universe expanded with 40 new unique sectors, additional trade goods, and new space stations. Another major introduction was the pirates, who now possess their own distinct ships and lawless sectors. Furthermore, players are no longer restricted solely to the X-Perimental Shuttle; instead, almost any spacecraft in the universe can be purchased or captured and piloted directly. However, the legendary X-Perimental Shuttle can be reclaimed upon completing the only major storyline objective in the game. This so-called "Perseus Mission" is offered during the late-game phase, provided that the player meets certain specific requirements.

Released in 2004, "X²: The Threat" continues the overarching storyline within the X-Universe. Players take on the role of pilot Julian Gardna, discovering during the course of the main plot that he is actually the son of the missing Kyle Brennan. While searching for his father, a dangerous new hostile alien race known as the Kha'ak is discovered.
The main campaign is expanded by various randomized minor missions and dynamic assignments. Alongside significantly improved graphics, the game introduced brand-new sectors, equipment upgrades, as well as new ship models and classifications (such as M6 and TP). Furthermore, spacecraft are no longer protected solely by energy shields, but also by a newly introduced hull integrity system. X² was also released for Mac and Linux platforms and received predominantly positive reviews from critics and players alike.

Released in 2005, "X³: Reunion" continues the storyline revolving around Julian Brennan and the ongoing war against the Kha'ak. The player's primary objective is to prevent a newly discovered, devastating weapon from being activated. A notable addition includes unique unclaimed ships and hidden cargo containers floating out in deep space. Furthermore, the game introduced independent NPC merchants as free traders, alongside massive battles against the Kha'ak or Xenon that players can actively participate in. Individual factories can now be linked together to form vast factory complexes. Additionally, various starting scenarios can be selected, with more becoming unlockable during advanced gameplay.
With the release of Update 2.0 in 2006, a powerful spaceship of the new M7 class was introduced. During the "Bala Gi Research Missions", players can acquire this unique vessel and establish their very own Player Headquarters, which allows them to build, repair, and spray-paint their own ships. Four new ships of the advanced M3+ class were also added to the fleet options.
One year later, Update 2.5 brought the first iteration of the Mission Director alongside the new Uplink feature, enabling players to export and compare their personal gameplay statistics with the global community online.

Released in 2008, "X³: Terran Conflict" expands the explorable universe by adding space sectors within the Sol system, reaching all the way to the Moon and Earth orbits. New gameplay aspects and mechanics were introduced, including fresh weapons, new ship classifications (M4+, M6+, M7M, M8, TM), wingmen, wing management, marine training, and the boarding of capital ships. It also featured automated traders that conduct business independently, as well as a flight school tutorial tailored for X-series newcomers. Alongside the main storyline — which officially introduces the Terrans as a playable faction—and randomized assignments, players can undertake missions for new corporate factions and companies that offer unique prototype ships as rewards. The starting scenarios from the predecessor were replaced by a selection of distinct plots, each containing its own storyline, missions, and objectives. Advanced players can unlock additional late-game plots that yield highly valuable rewards, ranging from the legendary X-Perimental Shuttle to a personal Player Headquarters or even an entire custom space sector.

Released in 2011, "X³: Albion Prelude" showcases an X-Universe in transition, preparing players for the drastically altered universe featured in "X Rebirth". It functions as a standalone add-on to "X³: Terran Conflict", yet delivers a wealth of new content, functionalities, and quality-of-life improvements. Alongside a fresh main storyline, the game introduced new sectors, additional spaceships, space stations, reconnaissance drones, and jump beacons. Furthermore, a dynamic Stock Exchange system and intense war-themed missions were officially implemented. Ships can now be grouped together into a unified fleet management system. Additionally, the user interface (UI) elements were redesigned to utilize the available screen space much more efficiently.

Released in 2013, "X Rebirth" was designed and developed completely from scratch. The title serves as a soft reboot for the franchise, following the conclusion of the original X-Trilogy with "X³: Albion Prelude". It remains an open-ended, dynamic game where the universe continuously evolves, even when the player is not present in a specific sector. "X Rebirth" introduced a brand-new user interface explicitly aimed at lowering the initial complexity for newcomers to the series. However, the underlying depth of the gameplay mechanics remained comparable to previous X titles. In this installment, the "Albion Skunk" is the only playable spacecraft available to the player. These comprehensive overhauls and drastic changes were not well received by many dedicated X fans, prompting Egosoft to deliver numerous subsequent patches, rebalances, and expansions to address the community's feedback.

Released in 2018, "X4: Foundations" allows players once again to personally pilot almost any spacecraft in the universe. Both ships and space stations are now constructed from individual modular components, and ship classifications have been streamlined into four distinct size categories. Various starting scenarios are available to choose from. For the very first time in the series, the simulated economy fully encompasses the entire NPC production chain as well. The new menu navigation is primarily operated using the mouse. The updated graphics, expanded gameplay possibilities, and the seamless transition between the game world and your ships were well received by the community. Following two major patches, player reviews shifted to being mostly positive.