Senior SaaS Architect / Founding Full-Stack Engineer for Multi-Tenant Business Operating Platform

We are building SEMATRIX Pro, a new multi-tenant B2B SaaS platform designed to become a unified Business Operating System for professionals and growing businesses. This is not a website project and we are not looking for a basic MVP built from templates. The platform will bring multiple areas of business operations into one connected system, including: • CRM & client management • Projects, tasks & workflows • Invoicing & financial operations • Employees & workforce management • Files & document management • Forms & e-signatures • Calendar & scheduling • Client portals • Reporting & dashboards • Workflow automation • AI-powered business assistance • Multi-business management The key architectural challenge is that these cannot operate as disconnected applications. Clients, companies, employees, projects, invoices, documents, communications, permissions and activity must share a properly designed business data foundation. We are looking for a senior engineer/architect who has personally built production multi-tenant SaaS applications, preferably CRM, ERP, accounting, fintech, workforce management, operations software or other complex B2B platforms. What we need from you You should be comfortable owning or leading: • SaaS system architecture • Multi-tenant architecture and tenant isolation • Database/domain architecture • Backend APIs and application services • Modern frontend architecture • Authentication and RBAC/custom permissions • Audit logging • Cloud infrastructure and deployment • Third-party integrations • Payments/subscriptions • AI/LLM integrations and tool calling • Security and data protection • Testing and CI/CD • Production monitoring and scalability We are not looking for someone who simply connects APIs together. We need someone who understands how to design a maintainable platform that can expand into many business modules over time. Initial engagement We plan to begin with a paid Technical Discovery & Architecture phase before committing to the complete development project. During this phase, the selected engineer will review our existing product specification and help define: • System architecture • Database/domain model • Multi-tenant strategy • Permission/RBAC architecture • Module boundaries • AI architecture • Integration strategy • Infrastructure/deployment architecture • Security considerations • V1 scope • Development milestones • Technical risks • Estimated development timeline and budget An important part of this exercise will be identifying what should be built internally, what should use established infrastructure/providers, and what should NOT be built in V1. Successful completion of this phase may lead directly into a long-term development engagement to build SEMATRIX Pro. Before applying Please provide examples of the most complex production SaaS platforms you personally helped architect and build. We are especially interested in seeing actual working products rather than only screenshots or landing pages. Please explain your exact role in each project and which parts of the architecture/codebase you personally designed or developed. Important: All project source code, repositories and company production infrastructure for SEMATRIX Pro must remain under company-controlled accounts.