GenThresh.com uses bls12-381 as implemented here to allow you to Generate, Sign, Aggregate and verify BLS signatures. It also allows for the spontaneous creation of rooms (using websockets) where users can automatically aggregate signatures.

GenThresh has NOT been audited and should be therefor not be used for highly sensitive data or financial usecases.

The code here is a prototype, management of the DOM without a framework is a mess, and the server-side script stores everything in memory which will not scale, i fully encourage someone to take this and iterate to a production ready app.