NFT Studio was created by me - an indie developer - under the name of 'StrangeWays'. It was created to make the creation of NFT collections cheap and accessible to all, as of now it is completely FREE! Screenshots further below.

StrangeWays Discord: https://discord.com/invite/pS3qhWBy9f

Features:

Unlimited collection size
Unlimited collections
Unlimited traits (depends on your RAM and the memory they take)
Uses a flowchart system with layer rarities
Traits have rarities
Advanced trait rules such as: Blocklists, Multi-Layer-Trait Configuration, Force Layer Traits, Max 'X' Spawns Per 'X' Generations
Multiple import formats: JPG. PNG & GIF
Multiple export formats: JPG, PNG, WebP & GIF (Animated/Non-Animated)
Set image quality
Set framerate for GIF's
Count all possible combinations (keep track of how many possibilites remain when generating)
Disallow duplicates (make sure the same image is never generated twice)
Metadata JSON files are created for your images
Generate one by one and be selective about which to keep/discard
Generate in batches (if you don't like some of the images you can delete them post generation and then use the 'Sweep Collection' function which will fix your images and metadata files by editing their names and the data inside of JSON files, effectively reorganising your collection and filling the gaps you created when you deleted the images)