It takes pictures from e621, then you vote if you like them or not and it gets better at guessing what you might like.

Keys:
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Space - Upvote AND Download
J - Upvote
K - Neutral vote
L - Downvote
Q - Skip batch.
Options.xml
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Here's the meaning of the different options in the .xml file.
Search tags: The string used to query the e621 api. It has a limit of 3 iirc.
BlackList: Pictures with any of these tags wont appear.
LastId: The id it will start the search from the next time.
BufferSize: Pictures stored in memory at the same time.
PicBatch: Number of pictures it will check each time it queries the api. I'm pretty sure there's a hard limit, so I wouldn't change it.
VotesNeeded: Number of votes a tag needs to have to be used in the calculus.
AgroLimit: Agro is a score increased each time you downvote or neutral a picture. It resets on a positive vote. If it reached this number, all remaining pictures are discarded and a new batch is loaded.
DownloadFolder: Relative route to the folder pics will be downloaded.