Scrips is a token system for crafting and gathering first introduced in Heavensward. You can earn Scrips by gathering or crafting Collectables after level 50.
Collectables can be turned in at any Collectable Appraiser. The Scrip Exchange, who sits next to the Collectable Appraiser, will accept your scrips and offer gatherer and crafter gear, Soul of the Crafter, Master Recipe Tomes, Tomes of Regional Folklore, gatherer and crafter Materia, and other tokens and crafting materials. Each expansion's appraiser and exchange has to be unlocked separately, and doing so adds that expansion's items to all exchanges.
The most recently retired scrip can be traded up for the next valid one at a 1:1 rate at the Scrip Exchange in Mor Dhona (X:22.4 Y:6.7) only. This is different from how retired Allagan Tomestones work.
Introduced in Patch 6.0 with the release of Endwalker, Purple Scrips are used to purchase endgame items at level 90.
Introduced in Patch 5.0 with the release of Shadowbringers, White Scrips are currently used to purchase all items up to level 89.
In a related way, the currency introduced in Patch 5.11 and earned from the Ishgardian Restoration is called Skybuilders' Scrip and is likewise earned by crafting collectables. However, the ingredients and recipes are unique to the restoration, and most materials are exclusively found in the latest iteration of the Diadem.
Introduced in Patch 4.0 with the release of Stormblood, Yellow Scrips were originally used to purchase endgame items at level 70. Weekly limits on all scrips were lifted at the same time. Yellow Scrips were retired with the release of Endwalker and are currently exchangeable 1:1 for White Scrips.
Introduced in Patch 3.05, Red Scrips were originally used to purchase endgame items at level 60 and initially weekly locked to 450 just like the most recent Allagan Tomestones. They were retired with the release of Shadowbringers and were exchangeable for Yellow Scrips until Endwalker launched.
Introduced in Patch 3.0 with the release of Heavensward, Blue Scrips were used to purchase items at levels 50-59. They were retired with the release of Stormblood and were exchangeable for Red Scrips until Shadowbringers launched.
In real life, Scrip systems are outlawed in many late-stage capitalist democracies because of their historical use in exploiting vulnerable employees.