independent development; in-house development
Used for technology, products, or systems developed by a company or organization on its own, without relying on external partners or off-the-shelf solutions.
This software is entirely developed in-house.
They announced a new technology developed independently.
独自開発 also means independent/original development, but 自主開発 emphasizes self-reliance and internal capability, while 独自開発 highlights uniqueness or originality.
Compound of 自主 (self-reliance, autonomy) and 開発 (development).