# Userspace

Gall is one of the nine vanes (kernel modules) of Arvo, Urbit's operating system. Gall's purpose is to manage userspace applications called *agents*. **Agents** are the main kind of userspace application on Urbit. They have a persistent state and API that handles events and produces effects.Gall agents can variously be treated as databases with developer-defined logic, services, daemons, or a kind of state machine.

One or more Gall agents can be put together in a "desk" in Clay (the filesystem vane) and, along with a front-end, can be published and distributed as a cohesive app for users to install.

This section of the docs contains guides related to writing apps and [distributing them](https://docs.urbit.org/build-on-urbit/userspace/dist/software-distribution). It also contains a number of different [examples and exercises](https://docs.urbit.org/build-on-urbit/userspace/examples) you can work through to learn how to build different kinds of apps.

Additionally, the [courses](https://docs.urbit.org/build-on-urbit/contents) section of the docs contain two in-depth app-building tutorials, which are the recommended place to start learning Urbit app development:

* [App School](https://docs.urbit.org/build-on-urbit/app-school) - Learn the basics of app development.
* [App School II](https://docs.urbit.org/build-on-urbit/app-school-full-stack) - Learn to build and publish a full app, back-end and front-end.