Yeah, I'm big on BDD. I'm doing it at my day job, as well, and already uncovered some major errors in the spec.
Domain Driven Design is one good discipline, i also found another one that is quite useful that nostr:npub1l5sga6xg72phsz5422ykujprejwud075ggrr3z2hwyrfgr7eylqstegx9z talks about a lot, Behaviour Driven Design
at my paid gig the guys who are building the back-end/middleware of our application use both of these techniques in their work also... i honestly haven't studied them hard enough, but i grasp the basic principles reasonably well
DDD is kinda like an elaboration of the Single Responsibility Principle and aims to help meld the expertise of subject matter specialists who have got less software engineering skills with the programmers, project management and ops people