Product Engineering Services (PES) encompass the entire journey of a product from conception to market release, covering design, development, testing, and beyond. It's a holistic approach aimed at creating a viable, usable, and desirable product. On the other hand, Custom Software Development focuses specifically on coding and creating software based on the unique requirements of a client, often without the broader scope of product lifecycle management. While both are essential in the realm of software solutions, PES provides a more extensive view, ensuring the product's success in the market, whereas custom software development is more about tailoring software solutions to specific needs.