Open Source Field Service Software
Field service software is judged at the worst possible moment - a technician standing in a basement with no signal, needing the work order, the asset history, and the customer's address right now - so the real test is how the system behaves when the network does not. The open source field service platforms here put the dispatch board, work orders, and technician scheduling on infrastructure you run, so the job data and customer records that drive every truck roll stay in a database you control rather than a per-technician subscription.

OCA Field Service
Odoo modules for field service management: locations, workers, orders, routes, and billing

Beveren FSM
Field service management app for ERPNext covering requests, scheduling, and invoicing

Open Field Scheduling
Self-hosted field service scheduling for jobs, customers, dispatch, and invoicing