[dschmidt]

Description

Adds web-app-apollon: collaborative UML diagrams in OpenCloud Web, built on the Apollon editor from TUM.

• Registers for .apollon files and adds a "UML diagram" entry to the "New" menu. A new file starts with a choice of diagram type (all 13 Apollon types).
• Collaboration through the Yjs session of the app wrapper, like the Excalidraw app: live sync, remote cursors, selection highlights, a presence bar and following a collaborator's viewport.
• Saving, the unsaved-changes guard and closing come from the OpenCloud frame. Read-only without write access, follows the light or dark theme.
• File format: the bare Apollon model as JSON, as the Apollon VS Code extension reads and writes it.

Screenshots

Apollon-2026-10-07_06.58.38.mp4

Notes

• Needs Web 8.1.0 or newer and @tumaet/apollon 5.4.0, the first release with my upstream changes for this app (feat(library): add editor-free model and Y.Doc helpers ls1intum/Apollon#858, fix(library): keep the remote cursor steady while the canvas pans ls1intum/Apollon#859, feat(library): accept a host-owned Y.Doc and awareness ls1intum/Apollon#860, fix(library): follow a single scroll step of the viewport ls1intum/Apollon#861).
• pnpm-workspace.yaml pins the transitive @xyflow/react to 12.11.1, as Apollon does because of a touch regression in 12.12.0, and declines the core-js install script of Apollon's optional jspdf.

Known limitations

• Two users changing the same element at the same time: the last change wins.
• A file that is not in the exact output format of the app can be shown as unsaved although nothing changed. The app wrapper compares the serialized text with the file content, so this is not specific to this app.
• Apollon's own labels are English only.
• No export to SVG, PNG or PDF.

Related Issue

None.

How Has This Been Tested?

• Against the published @tumaet/apollon 5.4.0: unit tests of the Yjs adapter (14), type check and the e2e test (create, choose a type, draw, save, reload) in Chromium and Firefox against OpenCloud 8.1.0.
• Manually with two browsers and two users, against a local Apollon build from before the upstream reviews (2026-10-07), not repeated with 5.4.0: live sync, cursors, selection and presence, following a viewport, read-only shares, public links (view and edit), theme switch, an external write to the open file, and a file that is not an Apollon model.

Types of changes

• Bugfix
• Enhancement (a change that doesn't break existing code or deployments)
• Breaking change (a modification that affects current functionality)
• Technical debt (addressing code that needs refactoring or improvements)
• Tests (adding or improving tests)
• Documentation (updates or additions to documentation)
• Maintenance (like dependency updates or tooling adjustments)

[JammingBen]

Works like a charm!

Could you please add a CHANGELOG.md file with version 1.0.0 so we can release it?

[dschmidt]

Thanks for testing! I added packages/web-app-apollon/CHANGELOG.md with version 1.0.0 in 923a686.