Nu – the interaction primitive.

Build apps in one primitive that spans your whole stack (databases, UIs, AI agents, and services). No glue. 50x less code.

Every app is a set of interactions between systems: a database, a UI, AI agents, and services. Nu makes interaction the primitive:

• Ref names what you touch. A KV slot, a UI widget, an LLM endpoint, a memory slot, a remote object.
• Interaction describes what to do with it. Read, write, branch, iterate, compose.
• Fabric binds Refs to a real backend. Swap the Fabric, keep the tree.

Persistence, reactivity, atomicity, observability, and scalability are inherent, not bolted on.

The interaction model

Nu, the one core atom, splits into two:

• Ref: address to any resource.
• Interaction: the work over Refs.

Compose them into a tree. That is a Nu program.

Example

A dashboard on a live counter that persists across restarts. One Nu tree, two Fabrics.

import nu


class Counter(nu.Shape):
    value: nu.v.IntRef


class Dashboard(nu.ui.Page):
    count: nu.ui.TextRef


class App(nu.ui.Index):
    pages = nu.ui.Pages({"/": Dashboard})


app = nu.With(
    nu.v.presets.rocksdb_navigator(".dbtest"),
    nu.ui.presets.server(
        nu.v.auto_flow_atomic(
            nu.ReactForever(
                Counter.value.on_change(),
                Dashboard.count.set(Counter.value),
            ),
        ),
    ),
    body=(
        nu.IfDo(Counter.value.missing(), Counter.value.set(0))
        >> nu.ForeverDo(
            Counter.value.inc() >> nu.Delay(1.0),
        )
    ),
)


if __name__ == "__main__":
    import asyncio

    asyncio.run(nu.arun(nu.v.auto_flow_atomic(app)))

Run it, open the browser tab. The counter ticks once a second, the dashboard mirrors it live. Kill it, run again, it picks up where it left off.

More examples in examples/. Full walkthrough at nustack.dev/docs.

Fabrics

A Fabric implements Refs against one backend. Nu ships five in-tree.

Fabric	What
nu.m	In-process substrate. Zero-config default for tests, notebooks, cache.
nu.v	Persistent substrate backed by virtuals. Virtual Python collections over RocksDB, LMDB, more.
nu.ui	Refs on screen. Binds Nu Refs to a live browser tab.
nu.invisibles	Location-independent Nus. Transparent RPC across processes and machines.
nu.ray	Compute across the cluster. Scale Nu on Ray without leaving the model.

Swap the Fabric, keep the tree. Same program runs against different substrates.

Install

Python 3.12+.

pip install "nustack-py[all]"

See nustack.dev/docs/how-to/install for lean installs and source builds.

Apps built on Nu

• nulog. Structured logging as a Nu app. Handles billions of entries, UI dashboard out of the box.

Status

Alpha. APIs will break.

License

Apache-2.0