0.31 (Early versions of Indev with "0.31" as the version number)
20091223-1 was the first version of Indev. It added ranas and smoother lighting.
20091223-2 was the second indev. It added torches.
20091231-1 was the third indev, and the first survival one.
20091231-2 was the fourth indev, and the last one of 2009, released 3 minutes before midnight. It added certain iron tools, the apple and armor from another game made by Notch.
20100105 was the fifth indev.
20100106 added level options.
20100107 added more level options.
20100109 added fire.
20100111-1 added the ability to use tools.
20100111-2 added fullscreen (F11)
20100113 made water finite.
20100113-c was a creative Indev released for testing finite water.
20100114 added the infinite water source block to the inventory.
20100122 made changes to water spawning.
20100124 added chests and a sound effect for arrows.
20100125-1 added certain particles.
20100125-2 added gears.
20100128 added a 3D likeness for items.
20100129 added diamond ore, diamonds and diamond blocks.
20100130 added beast boys and other mobs, that only existed in this version.
20100131 added steve mobs that could be hit.
Unpopular opinion: Minecraft was at its best during Alphas, and 0.0.14a gravel was the best gravel.