Can open source BMS replace a proprietary BMS entirely?

Sometimes. Greenfield sites can standardize on open source supervisory software plus BACnet/Modbus controllers. Brownfield sites often overlay open source analytics and IoT on existing proprietary head-ends, replacing functions incrementally rather than in one cutover.

What licence types appear in open source building software?

Common licences include Apache 2.0, MIT, GPL, and AGPL. Apache/MIT are permissive for commercial integrator products. GPL/AGPL may require source disclosure when you distribute modified software — legal review is essential before white-labeling.

Do open source BMS projects support BACnet and Modbus?

Support varies by project. IoT-centric platforms usually emphasize MQTT, HTTP, and LoRaWAN with BACnet/Modbus via gateways. Traditional automation runtimes often native BACnet/IP. Always verify the exact protocol list against your field devices.

Where does CONTEXUS fit?

CONTEXUS is an open source modular smart building framework — not a single monolithic BMS binary. Integrators combine Open IoT Hub, energy, analytics, 7D BIM, and other modules to match each client's BMS, BEMS, and digital twin requirements.

Open Source BMS Compared: Choosing in 2026

Why teams consider open source BMS

Predictable hosting costs instead of escalating per-point licences.
Freedom to customize dashboards, drivers, and integrations.
Auditability of security patches and protocol handling.
White-label delivery for system integrator and PropTech partners.

Evaluation criteria

Criterion	Questions to ask
Licence	Permissive vs copyleft; compatible with your resale model?
Protocols	Native BACnet, Modbus, MQTT, LoRaWAN, OPC-UA?
Deployment	Self-hosted, edge, hybrid cloud; HA requirements?
BIM / AI	IFC lifecycle, LLM analytics, digital twin roadmap?
Community	Release cadence, issue response, contributor governance?
Commercial support	SLA, professional services, partner programme?

Landscape by category (facts only)

Open source building software clusters into three buckets. Verify details on each project's official repository before specifying.

Building automation runtimes

Projects in this space target DDC-style control and scheduling. Check each repo for supported protocols and licence (commonly GPL or Apache). Example starting points: search for "open source BACnet stack" and "open source building automation" on GitHub — compare commit activity and maintainer responsiveness.

IoT / digital twin platforms

These emphasize device onboarding, rule engines, and dashboards over traditional BMS graphics. Representative open platforms include ThingsBoard (Apache 2.0) and openHAB (EPL-2.0). BACnet often arrives via gateways rather than native objects.

Home / light commercial automation

Home Assistant (Apache 2.0) excels at integrations and DIY deployments; enterprise BMS teams sometimes prototype here but usually move to multi-tenant, RBAC-hardened stacks for portfolio rollouts.

Decision framework

Scenario	Typical approach
Greenfield smart building	Modular open source stack + BACnet controllers
Brownfield retrofit	IoT overlay + analytics; keep existing BMS head-end initially
Regulated / healthcare	Emphasize audit trails, support SLAs, validated change control

Where CONTEXUS fits

BMS function	CONTEXUS module
Multi-protocol supervision	Open IoT Hub
Energy / ISO 50001	Energy Management
Analytics / LLM queries	AI Analytics
Lifecycle / spatial context	7D BIM platform
Concept primer	What is a BMS?

CONTEXUS is an open source smart building platform for integrators who assemble modules rather than reselling a single proprietary executable.