By late 2008, our founders had put together a detailed game design document outlining the plan for Path of Exile. Surprisingly many of the elements described in this document made it into the full game, including ones that were implemented many years after Path of Exile's release. Today's news post outlines the parts of Path of Exile that came from the original design, and draws attention to a few that we just didn't think of until later.

• Achievements/Challenges: Achievements were planned, but Challenges were not. We added these as a retention mechanic in our first Challenge League and found they worked well.
• Ambush: Yes. While the full league itself was designed in 2014, the concept of chests with mods on them (where half the mods are traps) dates back to the original design document. It was intended that chests of all types could be rerolled, but during Ambush's design we realised this wasn't ideal as it'd slow down gameplay too much to have to consider rolling each rock or barrel you came across.
• Anarchy: Yes. Rogue Exiles were an idea of Erik's that was intended from the start.
• Ascendancy Classes: No.
• Attributes: Yes. Strength, Dexterity and Intelligence were locked in from the start. The first design had them giving +1 life, +1 accuracy and +1 mana respectively.
• Auras: Not mentioned specifically in the original design document.
• Character Classes: Yes. The seven classes were planned from the start, even though the Scion wasn't announced and released until 2013. The original names were Marauder, Hunter, Witch, Swordsman, Trickster, Templar and Adventurer.
• Charges: Yes, though these were initially called counters. Our design doc is full of "adds frenzy counters" for example.
• Corrupted Side Areas: Something very close to this was mentioned in the original design document.
• Currency System: Yes. Almost all of the orbs are identical. A few were renamed (like Chaos Sphere -> Chaos Orb).
• Domination: Yes. Shrines were planned from the start. The Domination league established the rule that Shrines have to affect the monsters around them also.
• Energy Shield: Yes.
• Flasks: Yes, in their current form. We didn't have Utility Flasks planned. Initially, you'd refill flasks at Fountains rather than accumulating charges from monster kills. This led to Fountain-camping.
• Flavour text: Yes.
• Gold Coins: My initial answer to this was "They weren't in the design document and were later introduced in the Perandus League with a lot of care to give them uncertain value", but it turns out that the original design doc did have gold coins used as currency in the first couple of acts before being phased out. This was because we were worried that players would expect gold in the game and wouldn't play it if there wasn't any. Prior to implementing it, we cancelled this plan and went with the current currency system.
• Hideouts: No. Jonathan came up with these in 2014.
• Item Corruption (Vaal Orbs): No.
• Item Linking: Yes.
• Item Rarities: Yes. Normal/Magic/Rare/Unique were locked in from the start and we avoided the trap of trying to add an additional rarity tier (until Shaper/Elder items happened?)
• Jewels: No.
• Ladders: Yes.
• Leagues: Yes.
• Level Cap: Yes. The plan of harshly diminishing experience with a cap of 100 was intended from the start. It wasn't meant to be as fast as it currently is now though.
• Lockstep Mode: No.
• Map System: No. While the initial design did have the ability to "itemise areas and reroll mods on them", we didn't imagine it anything like the end-game map system. It was more of a thing where you can occasionally find an area with mods that you could itemise and trade.
• Masters: No.
• Microtransactions: Yes. While we didn't have the current wide selection planned, our monetisation strategy was locked in from the start.
• Mystery Boxes: No.
• Overlay map: Yes. Planned from the start, and actually almost unchanged from the initial version until 3.0.0!
• Passive Skill Tree: Yes, though the tree went through many iterations before it became what it is today. Initially you could put multiple points in each skill, and it was a long time before we broke the class start locations out to various places on the tree. This is worthy of its own news article at some stage.
• Prophecy: Yes. Prophecies were initially planned as "itemised quests".
• Quality: Yes, and it functioned in the same way on all item types (other than Maps which didn't exist).
• Resistances: Yes. Fire/Cold/Lightning/Chaos resistance were planned as they currently are.
• Respec points: Yes. The Orb of Regret was originally called the Orb of Correction.
• Sockets/Gems: Yes, but they worked subtly differently at first. If you supported the same skill with different support gems in multiple items, they'd all affect it. So you could triple-support a fireball in one item and pentuple-support it in another for a total of eight supports (or more). This encouraged one-skill builds and was changed to the current system where the gems must be in the same item.
• Stash Tabs: Yes, though it was a few years later that we planned the speciality ones like the Currency Tab.
• Status Ailments: Yes. They were the same as the current ones. Shock initially didn't stack in the original design. We added that before release, and removed it later. So it's back to the original plan now!
• Supporter Packs: No. We thought of these in 2012, inspired by crowdfunding sites.
• Ten Acts: No. This was decided in late 2016. Until then, we had five planned acts and a difficulty level structure.
• The Atlas of Worlds: No.
• The Labyrinth: No.
• The Pantheon: No.
• Totems: Yes. The decision to add a Totem Support Gem was made later.
• Trade Sites: No.
• Traps/Mines: Traps were planned at first, mines were not.
• Tutorials: No. The initial plan was that the game would be self-evident to play, but we now realise that players come from a variety of gaming backgrounds and tutorials really help those who aren't core ARPG gamers.
• Vaal Skills: No.
• Vendor Recipes: Surprisingly, no. This wasn't in the original design document, but was decided before release of the game.
• Waypoints: Yes, they're a genre staple.
• Weapon Swapping: Yes.

One day in the future, we may decide to share the full document, until then though, it's still a source of inspiration when designing new leagues and expansions for Path of Exile.