For key aggregation (multi-signature applications): https://medium.com/blockstream/musig2-simple-two-round-schnorr-multisignatures-bf9582e99295

For signature aggregation (combining signatures, a potential fork of Bitcoin that could allow you to provide only 1 signature for multiple inputs, reducing fees): https://github.com/BlockstreamResearch/cross-input-aggregation

shibe

Oh I did not know that. I remember listening to tadje dryja talking about that in 2019 on youtube but I guess he skipped that part for the sake of simplicity. Do you know a good resource for learning  about signature aggregation and proposals?