I am working for the past few months with collaborators (in cc) on providing Rust reference implementations to existing multi party schemes for Schnorr signatures [1]. This includes aggregated signatures, accountable signatures (which for n out of n are multi-signatures) and threshold signatures (wip). 

The project can be found here: https://github.com/KZen-networks/multi-party-schnorr . 

We aim that if the protocol is run in a configuration of a single party it will be bip-schnorr [2] compliant. 

[1] https://github.com/KZen-networks/multi-party-schnorr/tree/master/papers

[2] https://github.com/sipa/bips/blob/bip-schnorr/bip-schnorr.mediawiki