The structure of the gap is qualitatively different in office software from cloud. Here the core of substitution works well — Nextcloud with OnlyOffice or Collabora Online achieves high compatibility with DOCX, XLSX, and PPTX formats; resolves real-time collaborative editing; offers file sharing, versioning, comments. Quality has grown over the past five years and in 2026 is at a level that suffices for most ordinary enterprise office work.
The gap is in the second and third ring of integration.
What Microsoft 365 brings beyond Word/Excel/PowerPoint:
Outlook + Exchange
Two commercial European alternatives deserve special mention here, because they are not just individual components but complete suites comparable to Exchange + Outlook:
- IceWarp (Czech firm, headquartered in Prague, customers including the country's largest national airline) — an integrated server for email, calendars, tasks, TeamChat, video conferencing, file sharing, and document editing, with both cloud and on-premises deployment options. The Outlook Sync integration preserves the user experience familiar from the Microsoft environment.
- Proton Business Suite (Swiss firm Proton AG, 50,000+ organisations) — an end-to-end encrypted bundle of Mail, Calendar, Drive, Docs, Sheets, Meet, VPN, and Pass under Swiss jurisdiction (outside the EU but crucially outside the reach of the CLOUD Act), with SOC 2 Type II and ISO 27001 certification.
Smaller open alternatives — Nextcloud Mail, Thunderbird with calendar plugin, SOGo — are functional for less demanding scenarios. Gaps relative to Exchange: fine-grained delegation and complex meeting rules across the organisation, meeting-room booking at scale, specific integrations with CRM and ERP, and — for Proton — currently missing presentation software and a still-maturing spreadsheet application (Proton Sheets was released only in December 2025).
Teams
Alternatives: Nextcloud Talk, Element/Matrix, Jitsi, Rocket.Chat — all functional, but with less seamless integration to the rest of the suite.
SharePoint
Document libraries with advanced metadata, workflow, custom applications. Alternatives: Nextcloud's basic file management is advanced, but SharePoint has twenty years of intranet workspace development and the body of corporate applications that has grown around it.
Power Platform (Power Apps, Power Automate, Power BI)
Integrated low-code applications and automation. A comparable European alternative does not exist as a single bundled product. Low-code platforms (n8n, Appsmith, Budibase), BI tools (Metabase, Apache Superset), and workflow engines (Camunda) exist as open source, but integration between them is a do-it-yourself task.
Copilot
A generative-AI assistant directly inside Word, Excel, PowerPoint, Outlook, Teams. This is the main differentiator in 2026. Mistral Le Chat, Aleph Alpha Pharia, and other European AI assistants exist and function, but integration at the level of "an AI assistant inside every application" is in an early stage at European open-source office suites. Collabora and OnlyOffice both announce AI integration, but as of 2026 it is an optional connection to external models, not a peer-grade native product.
Practical implication
An organisation that today uses Microsoft 365 primarily for Word + Excel + PowerPoint + Teams + Outlook has a real migration path. An organisation that deeply uses SharePoint, Power Platform, and increasingly Copilot has a substantially more complex migration path — because that second and third ring of integration is exactly what makes Microsoft 365 an operating platform rather than just an office suite.
And yet migration is happening at scale. In 2025 and into 2026:
- Denmark announced a plan to replace Microsoft 365 across the public administration. , Danish department determined to dump Microsoft , 2025-06-13 · link · archived
- The German state of Schleswig-Holstein committed to migrating 25,000 government workstations from Microsoft Office to LibreOffice, from Windows to Linux, and from SharePoint/OneDrive to Nextcloud. , German state switches to LibreOffice, promises Windows move , 2024-04-04 · link · archived
- The Austrian Federal Ministry for Digital and Economic Affairs initiated a pilot of sovereign collaboration platforms.
- The French public sector, since the CNIL guidance of 2022, has progressively limited Microsoft 365 use, and several ministries operate Nextcloud for internal collaboration.
These steps are not marginal experiments. They are backed by legal analysis, public-procurement reviews, and concrete cost calculations. What is striking: the public sector, where integration with Power Platform and Copilot is less critical than format compatibility and collaboration, has an easier migration than the average private enterprise.