There are thousands of inhabited planets within the Milky Way, many of whom have native life while others have been colonized. Here's a list of some of the more well-known planets in the galaxy:
Terra: The home of the first humans to colonize the galaxy, the Terra system has a single habitable world, referred to as Terra IV, and a number of gas giant and smaller planets, much like Earth's solar system but with an asteroid belt closer to the sun than Terra. It has a full complement of climates and many different natural creatures that are very similar to Earthean animals.
Mythar: The humans of Terra were able to contact Mytharian High Elves with their powerful radio broadcasters, to which the High Elves replied via magical means. After jointly designing a ship which the Terrans used to reach Mythar II, the Golden Alliance was formed. The Mythar system has 2 inhabited planets, Mythar II and Mythar III. Mythar II's moon is composed primarily of Mahoucite, a material that is able to store and channel magical energy. Once every few years, the position of Mythar II, Mythar III, and Mythar II's moon are aligned in such a way that a mage of even low power can open a portal between the two planets. The Mythics and Redeemed of both planet have various claims over who is the true home species of the planet, though the only provable answer is that the Fairies are native to Mythar II, due to their unique reproductive process which involves the moon.
Duale: A planet of humans that was once divided by a fierce civil war, until an elemental named Megumi appeared. Megumi's message of harmony and peace spread through the world, uniting it long before the Golden Alliance allowed them in. When the Great Shift occurred and many humanoids of different races had a shape-shifting gene activated, they gladly accepted refugees from other planets that feared the unfortunate members of the new racial group. Duale's people sent emissaries to other planets in the region, the Elementals on that planet taking after Megumi's example, and were instrumental in the formation of the Elemental League.
Divina: The seat of the Angelic Protectorate is rumored to be the original home of the Divine and is the location of the AP's council. Many Divine believe that reincarnating in Divina's Holy Light will purify their bloodline and grant them a more proper new life.
Valhalla: Valhalla is home to the Valkyries, a peculiar sub-branch of the Divine. Valhalla has a mixed population of Divine(almost entirely valkyrie) and Human, and it is said that a Human on this planet who serves the higher powers that grant the Valkyries their strength may themselves be reborn as a Valkyrie, though the phenomenon is incredibly rare.
Pharadon: Pharadon III is a desolate, barely-habitable rocky world that the Anarchist Divine were teleported to and claimed as their new home. It is the home of the massive Entropy Generator that was once the Angelic Protectorate's teleporter, which has been modified to harness uncertainty to create enough power to keep the planet's massive dome shields active and protect the citizens of Pharadon from the brutal conditions outside the domes.
Vezzex: Another system in Galactic ANarchsit territory just bordering the Golden Alliance, its first planet was selected as the test site for the most advanced combat mecha yet developed, the Humanoid Robo-soldier Model 102. The Beta android was captured and had its code altered by Deviling engineers who created a virus that removed certain limiters in GA artificial intelligence programming, causing the test robot to gain self-awareness. The robot was destroyed from orbit, but the deviling scientists were able to harness the energy from the blast to send the virus through the entire galaxy using the subspace network. spreading sentience to mecha everywhere. Many mecha consider the crater where HR-102(b) was destroyed to be a site of reverence, and disallow nonmechanical visitors to the site, though some have theorized that this is because there may be the means at that site to create an antivirus that could suppress the mechas' sentience.
Earth 29: On the surface, Earth 29 appeared to be one of the most standard of Altearths, with a normalized timeline and standard historical figures all intact. Underneath this, however, is a network of vast conspiracies, with everything carefully engineered to appear normal but in actuality being manipulated by shadowy alien overlords. The most prevalent theory involves Uruseiyans who had contact earlier with other Altearths and gave future-historical information to Earth 29 in order to mess with them.
Earth 177: Earth 177 varied from the standard earths in the galaxy in that its history was altered dramatically after the second world war. Soviet forces counterattacked Nazi Germany, and occult artifacts that were uncovered were back-engineered to create "Red Tech", which the Soviet forces were able to use to great effect. This had the result of escalating what was a Cold War in standard Altearthean history into World War III. Professor Alba Q. Riley, working at M.I.T,, was able to replicate the technology with his own advanced scientific knowledge, but he disappeared when attempting to use an experimental teleportation device to reach Washington, DC. Still, his designs were put to great use, giving the United States the power needed to halt the Soviet invasion.
Earth 320(Planet Althea): Earth 320 was an unimportant Altearth which was scanned improperly and, due to a series of clerical errors mixed with the planet's human-caused pollution, was misclassified as uninhabitable among the BioGalactica Corporation's computers. When they fired a Galactic Seed at the world, the slime inside scanned the planet, determined that the most dangerous pollutants were the human occupants, and transformed the second human it encountered into Althea, the first Legion Queen, who began the Great Legion War. After Althea's suicide, Rose became the new Queen of the planet's Legion and rules with fairness, integrity, and peace. The world is a terraformed Gaia-class planet, with huge trees and beautifully sculpted land free of any pollution. Visitors are welcome but many are wary to venture into any Legion territory for obvious reasons.
Purraxia: Formerly named Ilithar by the Golden Alliance, Purraxia was found to house the most extensive sets of ruins dating back to Nekopotamian civilization, a spacefaring culture that spanned a number of systems in what is now primarily Golden Alliance and Castaways Treaty Systems space. More importantly, it was on this planet that a technologically advanced urn containing stasis-frozen cells of the Nekopotamian ruler, Princess Kasumi, was found, and from the study of these cells a large number of Demi-Humans were genetically spliced.
Uruseiya: The original home planet of the Uruseiyans, who controlled a number of planets in what would soon become Golden Alliance space. Their planets are notable in that they were all considered Watcher Protected, yet the Watchers did nothing as the Uruseiyans used their advanced spaceflight and magically-empowered technology to enslave or mess around with the other planets in their reach.
Ama: A planet inhabited by humans with a core composed primarily of mahoucite charged with entropic energy. Because of this, the planet's magnetic field inverts and tumbles at semi-random intervals, making most electrically-based technology useless and halting its development. Even though it is officially part of the Golden Alliance, it rarely has visitors because of the difficulties involved with getting a ship into its atmosphere. This planet is home to the Amazons, a matriarchal society with an emphasis on physical strength and shamanistic magical abilities.
Bish: An incredibly beautiful planet deep in Golden Alliance space, the equally beautiful Humans who arose here took to underground caves, initially to escape harsh UV radiation. Once they were able to scientifically reverse the damage done to their planet, they found it too beautiful to mar with cities and now leave the surface open only for incredibly expensive tourism.
Chib: A planet inhabited by diminutive Humans called Chibis, who once lived in fear of unspeakably adorable yet incredibly dangerous creatures. Now a part of the Golden Alliance, they are notable in their inversion of the standard perceptions of "cute" and "scary", which extends to the geography and flora of their planet, Chib.
Elstrange: A system with a single habitable planet with a largely mahoucite moon and a sun that would occasionally shift to a dim red, allowing the Vampire clans that normally stayed in the shadows and the other monstrous creatures that served them to hold centuries of dominion over the frightened humans there. It was here that Darkrider announced that he had discovered a way for Vampires to feed off excess magical aura energy from humans, rather than risk killing them outright through the draining of blood. The Vampire clans betrayed and murdered Darkrider for his "betrayal", but this spark was enough to shift the belief and better the relations between Vampires and non-Vampires throughout the galaxy.