Maybe industrial applications for dust-heavy environments or avoiding movable parts in a general make up most of the fanless niche, but some manufacturers offer

Maybe industrial applications for dust-heavy environments or avoiding movable parts in a general make up most of the fanless niche, but some manufacturers offer desktop-like system as well. Desktop-like because extensibility is limited: these systems are typically built around mini-ITX boards, and the passive cooling solution may have limited options for cooling SSDs. Sustained CPU performance can be quite good, particularly with the Intel T series or the AMD equivalent. DIY is a bit hit-or-miss because if you want a truly silent system, you need select components for absence of coil whine, and I haven't found a good way to do that yet.