# O21: a black-box remake of U95

> O21 rebuilds the 1995 Windows game U95 as an F# open-source remake. Its author describes a black-box process based on observing the running game and reading its data files; the current engine includes rendering, menus, bonuses and some enemy behaviour but is not yet playable.

- Type: Case study
- Targets: Game
- Category: Independent reconstruction cases
- Relationship: Independent reconstruction project
- Sources reviewed: 2026-11-06
- Added to the catalog: 2026-11-09
- Original resource: <https://github.com/ForNeVeR/O21>
- Primary source: <https://github.com/ForNeVeR/O21/blob/cad90840ce330e4c676e644c171d462d0f3784a5/README.md>
- Catalog page: <https://awesomerea.org/resources/o21-u95-case/>
- Record JSON: <https://awesomerea.org/resources/o21-u95-case/record.json>
- Chinese version: [简体中文](https://awesomerea.org/zh/resources/o21-u95-case/index.md)

## Requirements & limits

- **Prerequisites:** Original U95 resources are needed to run the game.
- **Prerequisites:** Development builds require .NET 10 SDK or later.
- **Limits:** The current implementation is not in a playable state.
- **License:** MIT license, except where individual files state otherwise.

## Primary sources

1. <https://github.com/ForNeVeR/O21/blob/cad90840ce330e4c676e644c171d462d0f3784a5/README.md>
2. <https://github.com/ForNeVeR/O21/blob/cad90840ce330e4c676e644c171d462d0f3784a5/CHANGELOG.md>

## More in Games

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- [Ocarina of Time: version 1.0 disassembly](https://awesomerea.org/resources/glitterberri-oot-disassembly-case/index.md) · Case study
- [open-iw: investigating Inner Worlds' packed game resources](https://awesomerea.org/resources/open-iw-inner-worlds-case/index.md) · Case study
- [Open1560: partial reconstruction of Midtown Madness build 1560](https://awesomerea.org/resources/open1560-case/index.md) · Case study
- [OpenBoxer: incremental reconstruction of Месть боксера game functions](https://awesomerea.org/resources/openboxer-case/index.md) · Case study
- [OpenDAoC: recreating a Dark Age of Camelot server](https://awesomerea.org/resources/opendaoc-core-case/index.md) · Case study

## About this entry

The description was reviewed against primary sources.
Original editorial content: MIT. Linked projects, papers and assets retain their own rights and licenses.