Add overview page

docs/overview.md

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 title: Technical overview
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+The Co-op Cloud is made up of a few simple, composable pieces. The system does not rely on any one specific implementation: each part may be replaced and extended as needed.
+
+- [Free software applications](#free-software-applications)
+- [The packaging format](#the-packaging-format)
+- [Container orchestrator](#container-orchestrator)
+- [Command-line tool](#command-line-tool)
+
+## Free software applications
+
+Applications that you may already use in your daily life: [Nextcloud], [Jitsi], [Mediawiki], [Rocket.chat] and [many more]! These are tools that are created by volunteer communities who use [free software licenses] in order to build up the public software commons and offer more digital alternatives.
+
+The communities who develop these softwares also publish them using containers. For example, here is the [Nextcloud hub.docker.com account] which allows end-users to quickly deploy a new Nextcloud instance.
+
+Learn more about why we use containers [in the FAQ section](faq/#why-do-you-use-containers).
+
+[nextcloud]: https://nextcloud.com
+[jitsi]: https://jitsi.org
+[mediawiki]: https://mediawiki.org
+[rocket.chat]: https://rocket.chat
+[many more]: /apps/
+[free software licenses]: https://www.gnu.org/philosophy/free-sw.html
+[nextcloud hub.docker.com account]: https://hub.docker.com/_/nextcloud
+
+## The packaging format
+
+The work required to take a new instance of an application and make it production ready is still too time intensive and often involves a duplication of effort. Each service provider needs to deal with the same problems: stable versioning, backup plan, secret management, upgrade plan, monitoring and the list goes on.
+
+Therefore, the Co-op cloud proposes a packaing format which describes the entire production state of the application in a single place. This format is based on the [standards based compose specification] which is most commonly used by the [Docker compose] tool.
+
+[Each application] that the Co-op cloud provides is described using the compose specification and makes use of the upstream project published container.
+
+Learn more about why we use Docker compose [in the FAQ section](faq/#why-do-you-use-docker-compose).
+
+[standards based compose specification]: https://compose-spec.io
+[docker compose]: https://docs.docker.com/compose/
+[each application]: /apps/
+
+## Container orchestrator
+
+Once we have our application packaged, we need a deployment environment. Production deployments are typically expected to support a number of features which give hosters and end-users guarantees for uptime, stability and scale.
+
+The Co-op cloud makes use of [Docker swarm] as a deployment environment. It offers an approriate feature set which allows us to support zero-down time upgrades, seamless application rollbacks, automatic deploy failure handling, scaling, hybrid cloud setups and maintain a decentralised design.
+
+Learn more about why we use Docker swarm [in the FAQ section](faq/#why-do-you-use-docker-swarm).
+
+[docker swarm]: https://docs.docker.com/engine/swarm/
+
+## Command-line tool
+
+Finally, with an application and an application environment, we need a tool to read that package format and actually deploy it to the environment. For this, we have developed and published the [abra] command-line tool.
+
+Abra aims at providing a simple command-line interface for managing your own co-operative cloud. You can bootstrap machines with the required tools, create new applications, deploy them, back them up, restore them and so on.
+
+[abra]: https://git.autonomic.zone/coop-cloud/abra
+
+## Moving forward
+
+Now that you've got an overview, it is time to [deploy your first application].
+
+[deploy your first application]: /deploy/