cottage industry
1. A small-scale industry carried out by people in their own homes. When my grandmother was a girl, she was part of a cottage industry that made textiles, along with the rest of her family.
2. A small (and often loosely organized) network or business. It looks like you guys have a nice little cottage industry raking leaves.
3. An area of study pursued by a few passionate people. I understand that not everyone is interested in tracing minute details in modernist texts, but it's a cottage industry for a few people in the Master's program, like myself!