Here are several leading software development firms in Sri Lanka (well-known for engineering capability, export services, or sizable local R&D). Short note on focus and location included — I cited authoritative sources for each.

• WSO2 — Open‑source middleware, API and identity platform vendor with major engineering operations and R&D in Colombo. (en.wikipedia.org)
• Virtusa (Sri Lanka operations) — Global IT services and digital engineering company with large delivery centers and R&D presence in Sri Lanka. (en.wikipedia.org)
• 99X Technology — Product engineering specialist (strong track record building commercial software products for ISVs; headquartered in Sri Lanka with large Colombo engineering team). (srilankabusiness.com)
• hSenid — Established Sri Lankan firm focused on HRIS, telecom and enterprise software plus outsourcing/managed services; multiple R&D centres in Colombo. (hSenid.com)
• MillenniumIT ESP (MIT ESP) — Enterprise solutions, trading/exchange platforms, systems integration and managed services with headquarters and sizable engineering teams in Colombo. (en.wikipedia.org)
• Zone24x7 — R&D and advanced technology centre in Colombo offering software product engineering, data science, embedded systems and IoT services. (zone24x7.com)
• Calcey — (Sri Lanka-based engineering teams) software product development and outsourcing for startups and enterprises (specializes in web & mobile product engineering). (srilankabusiness.com)

Notes:

• “Leading” can mean different things (largest revenue, export footprint, R&D headcount, product vs services focus). The firms above are prominent across those dimensions and commonly cited in Sri Lanka’s IT/export profiles. (en.wikipedia.org)
• If you want a tailored shortlist (e.g., for fintech projects, embedded/IoT, enterprise middleware, or hiring contractors), tell me the use case and I’ll refine the list and add contact/selection tips.