# Helio Sequencer: A GPL Piano-Roll Sequencer Built for Microtonal Music > Helio Sequencer is a free and open-source music sequencer for desktop and mobile platforms, developed under the GPL-3.0 license. It prioritizes a minimal interface and supports exotic scales and microtonal temperaments, with a built-in SFZ instrument player, a Lisp scripting layer, and translations into twelve languages. **helio-fm/helio-sequencer** — Libre music sequencer for desktop and mobile platforms - Repository: https://github.com/helio-fm/helio-sequencer - Website: https://helio.fm - Stars: 3,555 · Forks: 144 - Language: C++ - License: GPL-3.0 - Published: 2026-09-23 · Updated: 2026-09-23 · Language: en - Canonical page: https://hysenlabs.com/projects/helio-fm-helio-sequencer ## What Helio Sequencer Is and Its Design Philosophy Helio is described in its README as 'an attempt to rethink a music sequencer.' The three stated goals are a distraction-free interface, a preference for clarity over cleverness, and support for experimentation in areas that most sequencers leave underexplored, specifically exotic scales and microtonal temperaments. The project is developed by Peter Rudenko with contributions from a listed community. It is hosted at helio.fm, where prebuilt binaries are available for download. The documentation lives at docs.helio.fm. The GitHub repository is at helio-fm/helio-sequencer, with two active branches: master and develop. The README does not describe the piano-roll interface in prose, but the project description, the emphasis on scales and temperaments, and the CHANGELOG at the repository root indicate that it is a note-based MIDI composition tool rather than a digital audio workstation. Its intent is composition, not audio recording or mixing. The README links to a YouTube channel maintained by the project for showcasing Helio in use. This channel provides a more concrete picture of what the interface looks like and how it behaves during composition than the README text alone. Documentation at docs.helio.fm covers the getting-started workflow for new users. ## Platform Support and Getting the Builds The README states that Helio runs on desktop and mobile platforms. Prebuilt binaries are available at helio.fm rather than as GitHub releases (the repository has no GitHub releases listed). The CI configuration shows AppVeyor for Windows builds and Travis CI for other platforms, and build status badges for both the master and develop branches are displayed in the README. For developers who want to build from source, the README points to Docs/readme.md with a link to the #building-from-source section. The top-level repository structure includes a Source/ directory for the C++ source, a ThirdParty/ directory for vendored libraries, and a Resources/ directory. The Projects/ and Docs/ directories hold example project files and documentation respectively. The Packaging status section in the README links to a Repology badge, which tracks Helio's availability in various Linux distribution package repositories. This means some Linux distributions may offer Helio through their package manager. ## Microtonal Scales and the Core Design Distinction The README explicitly frames microtonal and exotic scale support as a primary design motivation. Conventional music software typically assumes twelve-tone equal temperament (12-TET) as the default tuning system, which works for most Western music but cannot represent scales with different interval structures, quarter-tones, or historic temperaments. Helio's approach is to treat scale and temperament as compositional parameters rather than fixed system properties. The README does not document the specific range of scales supported, but the stated goal is to 'encourage experimentation in underexplored areas in music, like exotic scales and microtonal temperaments.' This makes it directly useful for composers working in just intonation, maqam traditions, spectral composition, or any system that does not fit 12-TET. This distinguishes Helio from mainstream DAWs and piano-roll editors, which support microtonal tuning only through third-party plugins or per-note pitch bend workarounds. The README treats microtonal support as a core feature, not an add-on. The C++ codebase is organized under the Source/ directory, and the ThirdParty/ directory holds external libraries including the SFZ player code and the Lisp interpreter. Developers who want to extend the scale support would start in Source/. ## Built-in SFZ Instrument, Lisp Scripting, and Metronome Helio includes three built-in audio components. The first is an SFZ player based on SFZero, written by Steve Folta and extended by Leo Olivers and Cognitone under the name SFZeroMT. The README notes this as the 'built-in SoundFont player instrument.' SFZ is an open format for sample-based instruments, and this player allows Helio to produce audio using sample libraries without external plugins. The specific range of SFZ features supported is documented in the Docs/ directory, not in the README. The second is a scripting language based on a Lisp interpreter by Adam McDaniel (the wisp interpreter). The README calls it 'the built-in scripting language.' Lisp-based scripting gives composers a programmable layer for generating or transforming note patterns, which is a capability uncommon in consumer piano-roll tools. The third is a built-in metronome. The metronome sounds were recorded by Ludwig Peter Müller and are distributed under the CC0 license, meaning they are in the public domain and can be used and modified without restriction. The app icon is by Valery Davletbaev under a CC-BY license. Other icons come from free icon fonts licensed under SIL Open Font License and CC-BY. These separate licensing terms mean that anyone distributing a modified version of Helio must track which components fall under GPL-3.0 and which under CC-BY. ## Ardour as an Alternative and GPL-3.0 Implications Ardour is a free and open-source digital audio workstation that runs on Linux, macOS, and Windows. The key difference from Helio is scope: Ardour is a full DAW for recording audio tracks, editing, mixing, and applying effects. Helio is a piano-roll composition tool with no audio recording capability. A producer who needs to record a vocalist, layer audio samples, or mix a finished track needs Ardour or a similar DAW. A composer who wants to write MIDI-based music in a clean environment, with microtonal scale support, is the audience for Helio. The GPL-3.0 license covers the application source code. Under GPL-3.0, anyone who distributes a modified version of Helio must release the source code of their modifications under the same license. The documentation, translations, and logotypes use CC-BY. The metronome sounds use CC0. These three licenses cover different parts of the repository, so contributors and distributors need to be aware of which license applies to which component. ## Translations, Community Support, and Active Maintenance Helio's interface has been translated into twelve languages, with named contributors for each. The languages covered are Afrikaans, Chinese, German, Greek, Italian, Japanese, Korean, Polish, Portuguese, Turkish, Ukrainian, and Vietnamese. The README invites further proofreading and improvement at helio.fm/translations, suggesting that translation contributions do not require a code pull request. Financial support for the project is solicited through two platforms: Patreon (at patreon.com/peterrudenko) and OpenCollective. The README also includes a DigitalOcean referral link for infrastructure support. The project has no corporate backer mentioned in the README, so sustainability depends on direct user contributions. The last push was on 2026-09-22, which confirms the project is under active development. The default branch for active work is develop; the master branch appears to track stable releases based on the CI badge configuration. The repository does not have GitHub releases, so stable versions are distributed through the helio.fm website rather than through GitHub's release mechanism. Contributors who want to track breaking changes should consult the CHANGELOG.md file at the repository root, which documents changes between versions. ## Conclusion Helio Sequencer fits composers who want a piano-roll tool that handles microtonal scales without additional plugins, and who prefer a minimal interface over a feature-heavy DAW. It is the wrong tool for producers who need multi-track audio recording, mixing, or effects processing: those workflows belong in a DAW. Before committing to it, build from source or download from helio.fm and confirm that the SFZ player works with your specific soundfont files, since the built-in instrument is based on an extended fork of SFZero and its compatibility range is documented in the Docs/ directory rather than in the README. ## FAQ ### Does Helio Sequencer support microtonal scales? Yes. The README identifies support for exotic scales and microtonal temperaments as a primary design goal, distinguishing Helio from sequencers that assume twelve-tone equal temperament as the only tuning system. ### Where do I download Helio Sequencer? Prebuilt binaries are available at helio.fm. The GitHub repository has no releases; all distributed builds come from the project website. ### What license does Helio Sequencer use? The application source code is licensed under GPL-3.0. Documentation, translations, and logotypes use CC-BY. The built-in metronome sounds use CC0. The app icon is separately licensed under CC-BY by its author. ## Sources - [helio-fm/helio-sequencer on GitHub](https://github.com/helio-fm/helio-sequencer) - [Issues](https://github.com/helio-fm/helio-sequencer/issues) - [License: GPL-3.0](https://github.com/helio-fm/helio-sequencer/blob/develop/LICENSE) - [Project website](https://helio.fm) - [README](https://github.com/helio-fm/helio-sequencer/blob/develop/README.md) --- Hysen Labs editorial analysis, written from the project's own repository and release notes. Cite the canonical page: https://hysenlabs.com/projects/helio-fm-helio-sequencer