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.

A tiny program is a joy to write. Three lines, one substrate:

a = 2
b = 5
print(a + b)

Real apps don't stay here. a moves into a database. b comes from a form submission. The result renders in a browser. A background job reruns it when either input changes. Three lines become three hundred: an ORM, a request handler, a template, a websocket, a queue. Almost none of it is about a + b anymore — it's all interaction between substrates.

Nu makes interaction the primitive.

• Ref — a name for a value, wherever it lives. A KV slot, a UI widget, an LLM endpoint, a remote object.
• Interaction — what you do with a Ref. Read, write, branch, iterate, compose.
• Fabric — binds Refs to a real backend.

Same program, a and b persisted in a KV store:

import nu


class DB(nu.Shape):
    a = nu.kv.IntRef.slot()
    b = nu.kv.IntRef.slot()


# compute a + b and print it
compute = DB.a.set(2) >> DB.b.set(5) >> nu.print(DB.a + DB.b)

# assemble: rocksdb-backed
app = nu.With(
    nu.kv.rocksdb_navigator(".dbsum"),
    body=nu.kv.auto_flow_atomic(compute),
)

nu.run(app)

Same program, result rendered in a live browser dashboard:

import asyncio
import nu


class DB(nu.Shape):
    a = nu.kv.IntRef.slot()
    b = nu.kv.IntRef.slot()


class Dashboard(nu.ui.Page):
    out = nu.ui.TextRef.slot()


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


# compute a + b and render into the dashboard text block
compute = DB.a.set(2) >> DB.b.set(5) >> Dashboard.out.set(DB.a + DB.b)

# assemble: rocksdb-backed, served over the browser
app = nu.With(
    nu.kv.rocksdb_navigator(".dbsum"),
    nu.ui.server(nu.kv.auto_flow_atomic(compute)),
)

asyncio.run(nu.arun(app))

Same primitive, different substrate. One Ref for any resource, one Interaction for any op. Nu doesn't care what the backend is.

Persistence, reactivity, atomicity, observability, distribution — not features Nu has. What falls out of naming interactions instead of executing them:

• Persist across restarts — the KV slot is already durable.
• Re-render live on input changes — wrap in a React interaction.
• Handle terabytes — shard the KV Fabric; the Refs don't notice.
• Run distributed across a cluster — bind through nu.ray; the Refs don't notice.

Full walkthrough at nustack.dev.

Three steps: install, run a demo, explore Nu.

Python 3.10+ · everything ships in the wheel.

pip install "nustack-py[all]"

Each one boots a live browser dashboard and picks up where it left off on restart. nu demo lists them all.

counter	sampled
A live counter, persistent across restarts. nu demo counter	An infinite series, live-sampled into a line-chart. nu demo sampled
movies
A movie tracker: form, filterable table, detail pages. nu demo movies

• Read the docs — tutorials, how-tos, and the fabric reference.
• Browse examples — full source for every demo, plus more programs to steal from.

Each fabric binds Refs to a real backend and unlocks a new capability.

End-user tools written as Nu programs.

Nu is a reference implementation of the interaction model — a language-agnostic specification of what an interaction is, how Refs name locations, and how Interactions compose into programs.

nustackdev/interaction-model

TODO.

Add a Nu badge to your README if you're building on Nu:

[![Nu](https://img.shields.io/badge/built%20with-Nu-%237A4CE0)](https://github.com/nustackdev/nu)

Considering contributing to Nu? Start by opening an issue or a PR — the codebase is small and readable, and the model is stable enough to build on.

1. Read the docs
2. Open a feature request or report a bug
3. Join the Discord community

Apache-2.0