reactos-nitro is an unofficial patch set for ReactOS. It is not affiliated with or endorsed by the ReactOS project. ReactOS is a trademark of the ReactOS project.
Do not report problems from this build to the ReactOS project. Report them here, in this repository's issues.
Like ReactOS itself, this is alpha-quality software. Don't use it on a machine or disk holding data you care about.
Last synced with ReactOS master: e46f4bb1a1e (2026-10-25, sync #4). We merge upstream regularly; this line tracks the most recent merge. (nitro-2026.10-5 is based on this commit; nitro-2026.10-2 to -4 on f53b1d15601; nitro-2026.10-1 on the earlier ac1ab9e3043.)
Docs: CHANGELOG · BENCHMARKS · UPSTREAM
reactos-nitro is a large set of fixes and features maintained on top of upstream ReactOS master. Each release ships:
- the patch series: one patch per topic, plus the exact upstream ReactOS commit it applies to;
- build scripts that apply the series to a clean upstream checkout and build the ISOs;
- ready-to-install ISOs for amd64 (with WoW64) and i386;
- the full source tree of the release, tagged in the development fork.
See UPSTREAM.md for how reactos-nitro relates to upstream ReactOS and why our NTFS is a separate driver.
- Usable for daily work: real applications installed and running reliably, not only demos.
- Fast: responsive on modern multi-core machines and virtual machines.
- Secure: fix the security problems we find, and say plainly where protection is still missing.
- Actively developed: frequent releases, each one tested and documented.
- In sync with upstream ReactOS: track ReactOS master closely and merge it regularly. Keep our changes small and self-contained where possible, so the patch set stays easy to rebase and our fixes are easy to port.
Latest build: reactos-nitro-2026.10-5 (2026-10-29), on upstream base e46f4bb1a1e — the modern-app release: Windows 10 is the default reported identity; Chrome (software rendering) and Claude Desktop run; 32-bit Firefox renders at the default sandbox again (32-bit + 64-bit side by side); Firefox 158 and PowerShell 7 run; plus Task Scheduler 2.0, a guest-clock fix and a memory commit cap. Each release ships an amd64-with-WoW64 ISO, an i386 ISO, a source tarball, and the patch series; see CHANGELOG.md for per-release detail and known limitations.
Over 750 fixes and several feature tracks on top of upstream ReactOS:
- 32-bit Windows programs on 64-bit ReactOS (WoW64). Total Commander runs 32-bit and 64-bit side by side in one session, and Firefox runs 32-bit and 64-bit side by side at its default sandbox setting. Upstream ReactOS has no WoW64.
- Modern apps. Windows 10 identity by default; Chrome (software rendering) and Claude Desktop run; Firefox 158; PowerShell 7; Task Scheduler 2.0; an Optional Features manager.
- NTFS read/write, with a new driver built on the Linux kernel's
fs/ntfs(imported from Linux v7.3-rc6), plus journal and power-cut recovery. NTFS is the default file system for new installs. - Btrfs: WinBtrfs 1.10 (upstream ships 1.8.1).
- Multi-processor support on x86 and amd64, installed by default on ACPI machines. It is tested from 1 to 16 vCPUs, with multi-hour soaks on AMD and Intel hosts.
- Smoother desktop. A shadow framebuffer makes window dragging smooth at a fraction of the CPU cost. USB tablet polling and pointer fixes also help.
- Networking: a reworked receive path and dozens of TCP/IP, AFD and Winsock fixes.
- Setup and user profiles: the setup program preselects NTFS. The C:\Users layout includes Windows-style legacy folder links, and profile deletion works.
- Kernel and memory manager hardening: commit charging with a commit limit, plus many Mm, cache-manager and scheduler fixes.
- Desktop and tools: LCD text rendering, bundled open fonts, crash reports with a Windows-style dialog, and Disk Management.
A preliminary BENCHMARKS.md (draft) compares reactos-nitro against upstream ReactOS.
A full list of changes, one line per fix, is in CHANGELOG.md .
- WoW64 is amd64 only.
- Firefox sandbox. On 64-bit, the sandbox process starts but its restrictions are not fully enforced on ReactOS. 32-bit Firefox renders at the default sandbox setting.
- Software rendering only. Chrome runs with software compositing (no DirectComposition, no hardware GPU acceleration).
- 32-bit MFC applications fail at their first window (WoW64 global-hook gap).
- Memory commit is capped at about physical RAM until private memory is pageable; Firefox 128 x64 thrashes at the cap.
- .NET Framework 4.x managed applications do not run yet.
- Known open security hardening items (local-privilege class) remain; do not expose this to untrusted local users.
- Some 32-bit applications leave redraw artifacts when dragged over other windows.
- Tested Firefox versions: ESR 128 and Firefox 158. Newer versions are expected to work but are untested.
- Everything in upstream ReactOS's own list of known issues also applies.
The desktop shows ReactOS (Nitro) - <version>. The About dialog also says "Unofficial build, not supported by the ReactOS project".
reactos-nitro is distributed under the same licences as ReactOS: mainly GPL-2.0-or-later, with per-file licences kept as they are in the source. Upstream copyright notices are kept intact.
Credit goes to:
- the ReactOS project and its contributors, whose operating system this builds on;
- the authors of the Linux kernel's
fs/ntfsdriver; - WinBtrfs by Mark Harmstone;
- the Wine project, whose code ReactOS and this patch set reuse.