Here’s a curated shortlist of highly regarded custom software development firms with a strong Australia presence (mix of Australian-headquartered firms and global consultancies with major AU teams). I’ve grouped by scale and included one-line strengths + a source so you can check portfolios and recent reviews.

Enterprise / large consultancies

• ThoughtWorks — global technology consultancy with substantial Australian teams; strong in complex custom engineering, cloud migration and GenAI/product delivery (named a Visionary in Gartner’s Magic Quadrant for custom software services). (ThoughtWorks.com)
• Telstra Purple — Telstra’s large, Australian-owned technology services business (end-to-end cloud, data, security and custom software delivery with thousands of practitioners across AU). Good for large-scale, sovereign and telco-grade projects. (telstrainternational.com, Telstra.com.au)
• Accenture (Australia) — global systems integrator and engineering organization with deep local delivery, product engineering and AI teams for large enterprise transformation. (Accenture.com)
• Deloitte Digital / Deloitte Software Group (Australia) — end-to-end product engineering, AI and platform teams for enterprise digital transformation and custom platforms. (Deloitte.com)

Mid‑market & specialist Australian firms

• EB Pearls — large Australian-headquartered product and custom-software agency (mobile, web, AI-enabled apps) with extensive AU portfolio and strong Clutch presence. Good for product builds and fast-moving digital teams. (ebpearls.com.au)
• Appetiser — award-winning Australian app & product studio (mobile-first product design + engineering); repeatedly ranked among top Aussie mobile/app developers by Clutch/industry lists. (Clutch.co, Appetiser.com.au)
• Outware Mobile (Arq/associated) — long-running Melbourne studio focused on mobile-first custom apps for large Australian brands and government. Strong mobile portfolio (ANZ, Coles, AFL, etc.). (Clutch.co, crn.com.au)
• WorkingMouse — Brisbane-based software company focused on legacy-modernisation, secure onshore delivery and government/enterprise systems modernisation. Good for mission‑critical public sector projects. (WorkingMouse.com.au)

Nearshore / distributed and niche engineering teams with AU offices

• Fingent (Australia) — international custom-software and enterprise app developer with an Australian office; offers cloud, AI and integration services and enterprise apps. Suited for mid-to-large enterprise projects. (Fingent.com)
• Azumo — nearshore/nearshore-aligned software engineering & AI specialists with a Sydney presence / distributed teams; good for scalable engineering teams and AI-enabled products. (Azumo.com)

How to pick from this list (quick checklist)

• Match scale & domain: choose an enterprise consultancy (Accenture/Deloitte/Telstra Purple/ThoughtWorks) for large, regulated or highly integrated programs; choose mid‑market studios (EB Pearls, Appetiser, Outware) for product/MVP/web & mobile apps.
• Check recent case studies, references and security/compliance posture (ISO, SOC2) for sensitive data projects.
• Ask about team model: fixed-price vs. time & materials, onshore vs. nearshore, dedicated product team, and SLAs for support/maintenance.
• Verify tech fit: request examples using the primary stack you need (e.g., React/Node, .NET, Java, cloud provider, ML/AI).
• Get a short trial/PI or discovery sprint to validate delivery approach before committing to a long contract.

If you want, I can: (a) narrow these to the 3 best fits for a specific project type (enterprise platform, mobile product, AI/ML app), or (b) draft a 1‑page RFP/discovery brief you can send to them. Which would you prefer?