Calcumber
FreeUnit-aware engineering calculator — write calculations with real units (inch, kg, °C), named variables, and thermodynamic fluid properties. Share any calculation as a link, export to Word and Excel. Runs in the browser, installs to desktop, works offline.
How to install Calcumber as a PWA
Why we recommend Calcumber
Most calculators make you throw away the units and hope you kept the conversions straight in your head. Calcumber keeps units first-class through the whole calculation: give it an area in square inches and a paper weight in g/m² and it converts, checks dimensional consistency, and returns the result in the unit you asked for. That one design decision catches the class of errors that actually burns engineers — mixing metric and imperial, dropping a per-square-metre, squaring a length that was already an area. Around it sits a journal-style workspace (calculations read like a document, not a register tape), named variables that cascade through later lines, and a built-in fluid-properties library for thermodynamic work — the data you would otherwise dig out of steam tables. Every calculation is encoded in its URL, so sharing a worked example is literally copying a link, and the recipient can edit it live. Built by MFis GmbH in Switzerland, it installs from the browser or the Microsoft Store and keeps calculating offline.
Best use cases
Best for: mechanical and process engineers doing sizing calculations across mixed unit systems, engineering students sharing worked solutions (the whole derivation lives in the link), HVAC and energy work needing quick fluid-property lookups without a steam-table PDF, and anyone turning calculations into deliverables — the Word and Excel export makes a journal report-ready. The URL sharing is uniquely good for teaching and for reviewing a colleague's calculation.
Honest limitations
Not a CAS: it evaluates numeric calculations with units — it won't do symbolic algebra or calculus like Wolfram Alpha. Not a spreadsheet: for large tabular models with hundreds of rows you still want Excel; Calcumber is for the derivation, not the dataset. The fluid-property library covers common engineering fluids rather than exotic mixtures. The interface is desktop-first — it works on phones, but long journals are more comfortable on a bigger screen.
More in Productivity
The open-source web editor for slide decks — create, present, and share presentations from the browser, with live audience interaction. The project is now archived: the hosted editor is offline, but the code remains open source and self-hostable.
End-to-end encrypted office suite — docs, spreadsheets, kanban, code pads. No account needed for guest use. Hosted in France, GDPR-native. The privacy-first Google Docs alternative.
Open-source office suite with pixel-perfect DOCX/XLSX/PPTX compatibility. Self-hostable or cloud. The best free replacement for Google Docs when you need perfect Microsoft format support.
Open-source spreadsheet-database hybrid — like Airtable but self-hostable and free. Build relational tables with formulas, linked records, and custom views without monthly fees.
Local-first Notion alternative that stores notes as plain Markdown files directly on your disk. No cloud sync required. Your notes are yours forever — open in any editor.
AI-powered workspace for tasks, mind maps, and real-time collaboration. Installs as a PWA with full offline support. Combines the best of Notion, Trello, and a task manager.