The .blend files are Blender projects.
To use emote_creator_bend_item_scale.blend you need Blender version at least 5.0. For emote_creator and emote_creator_bend you can use Blender version from 2.83 up to 4.x. Emotecraft wiki if you're stuck.
.bbmodel files are models for Blockbench. You can use them as well.
To use them, you'll need to install the GeckoLib Blockbench plugin first.
The Blockbench emotes support is not very good on MC versions <1.21.7
Models labled with _bend allow you to bend some bones like in Minecraft Story Mode, and the rest of the labels should be self explanatory. Keep in mind that the visual for bending is incorrect in Blender/Blockbench, there won't be any gaps created by bending a bone in-game.
All Blockbench models support scaling.
Warning
Scale animation will be visible only on Minecraft version 1.21.4+
Tip
It's possible to add custom bones to a Blockbench model in order to animate player accessories IF it's supported by playerAnimator or another mod.
For example you can add a bone called elytra to the model and animate the elytra that way!
Cape rotations are also applied to elytras, but there won't be any bending.
The elytra bone's priority is greater than cape bone's for animating elytra but both can influence the elytra at the same time.
You can create your own program or edit the file by hand
The emote format documentation is here
Here is a Blender addon that lets you import and save animations + bend limbs on multiple axes.