Lore, while not the main focus of Planet Crafter, is an important part nonetheless. Here's what is known so far:
The Beginning[]
You are a prisoner who has been assigned to be a Planet Crafter that has been sent to an unnamed planet in a system used regularly for travel, and so the planet has recently become of interest. The reason you were sent here by a company named Sentinel Corp. (presumably a tech baron, or land developer) was to serve your sentence as a convict from an unknown home planet, instead of jail time (or whatever punishment you were originally going to endure).
Riley[]
However, you have someone on the outside, slowly leaking information to you. Their name is Riley. We know Riley and (Player) have met in the past, as stated in one of the communications received through the terminal. While they do send information, it is intercepted and encrypted, leading to info loss. Riley is not the only person that is referenced, because you are not the first planet crafter to go to this planet. On your behalf Riley will coordinate a covert extraction with Smugglers to get you off-world, for a price.
Messages[]
You will be sent messages from multiple sources via your 
Screen - Transmissions. Additional messages stored on datapads and computer terminals can be found throughout the planet.
Xiaodan[]
There is another prisoner named Xiaodan, who has secret bunkers scattered across the map. Xiaodan, even though clearly with plenty of resources, dies of unknown causes. His body can be found in a secret cave.
Convict GP-8971-Y[]
The message from Convict GP-8971-Y
There is one more character in the game, Convict GP-8971-Y, who sends you a message regarding their status as a nearby Planet Crafter. There is currently no way to interact with them.
Sentinel Corp. Messages[]
The Planet Crafter system is mentioned by automated messages from Sentinel Corp. Messages are sent as you progress throughout the game with additional information regarding upgrades, your status, and the planet's conditions. There is currently no way to interact back with Sentinel Corp.
The Final few messages received from Sentinel Corp. are stated as "This Is Not An Automated Message"; Implying as terraformation is nearing completion, the company is keeping an eye on you.
Ikhlas[]
Another known part of lore is Ikhlas (gender unknown). They weren't a Planet Crafter, but a traveler from a spaceship that crashed, due to the Warden Device, in the Dune Desert. They, being the only one survivor from their crew, tries to survive on the planet by finding resources, building bunkers with messages inside and trying to escape the planet using an 
Extraction Platform. It is unknown if they are still alive, or succeeded in extraction.
The Mysterious Door[]
This door can be opened with Warden Keys, allowing access to an alien structure behind it. This is a remnant of the Warden civilization and contains messages left over from that era.
Wooden Structures[]
There are artificial wooden structures in the Mushroom River. There is a message on one of them, sent by a "Warden". All of those wooden structures were probably also built by the Wardens.
The Wardens[]
An ancient, intelligent race, that tried to hide on this planet from the humans. Their social structure is that almost of a hive mentality;
"« The self should not exist ». That’s what we have been told since we are born.« As one, we live ». We, the wardens, are one, united, without individuals in the group. Does the concept of a group can even exists if there no entities?" -Message left by Wardens
They have built secret locations guarded by big stone doors operated by altars. They have left messages granting insights in their society and culture. Messages left by Wardens describe a brewing civil war between conflicting factions of the group deciding how to handle an impending catastrophic Meteor strike; One is adamant on dying on-planet, believing this to be their destiny. While the opposition are positive that their fate is not death, but to continue their civilization elsewhere among the stars. The latter have historical precedence because on at least one other occasion their society fled this planet before calamity struck, and returned when it was safe to do so.
The fact that one of the Game Endings explicitly states "Leave the Planet, trust that some of the Wardens are still alive, and accept you." it is likely there is no definitive in-game explanation as to the fate of every Warden. Given that their messages describe that the humans they met looked very much like them and the fact that you are able to read their messages, it is possible Wardens were a lost human colony that forgot its origins.
Physiology/Appearance;[]
Identical to Humans.
Conflict with Humanity; The Great Migration[]
Treha, The Warden's previous home planet was a flourishing world where the Wardens worked as one to create their ideal society. When humanity arrived, looking as Wardens did, they were welcomed in. However after realizing Humans were not mentally like the Wardens it became clear that the two; Human and Warden, could not peacefully co-exist, a few years passed, and as soon as they were able, the wardens fled their world, retreating to the prison planet (Player) find themselves on.
Warden Defensive Device[]
in an attempt to prevent humans from approaching this new planet, the Wardens set up a device that absorbs power from starships and blocks communications between human devices.
"Orbital drainage - defense device. Observation log:
The device is working as intended and our test are conclusive.
If ever the one calling themselves Humans approach this planet, it will drain the energy of their ships and prevent them from communicating."
This device is still active when (Player) arrives on the planet, and is responsible for the numerous crashed Human shipwrecks the player finds along their journey. The Device acts as a final obstacle to extraction,
Likely Cause of Planet Desolation[]
Through context clues from messages left by The Wardens, we can safely assume the planet was habitable in the past, and due to a catastrophic meteor strike, the planet's ecosystem, atmosphere, and the Wardens' civilization, (as well as any above ground evidence of their existence,) were destroyed.