Biography
Thomas Jaeger has been writing software professionally since 1991. His career spans MS-DOS, Windows, mobile, and cloud, across defense, finance, healthcare, professional sports, retail, and government work for clients including American Airlines, UBS, PayPal, Capital One, AWS, the NFL, and Royal Caribbean.
Thomas Jaeger, founder of Legacy to Modern LLC, has over 40 years of software experience. Starting his programming journey in 1984 with an 8-bit Z80 Amstrad CPC 464, he now specializes in modern software architecture: Domain-Driven Design, Command Query Responsibility Segregation, and Event Sourcing.
His career spans 14 industries: real estate, criminal justice, retail, banking, manufacturing, automotive, legal, aviation, travel & leisure (cruise industry), wealth management, electronic payments, health sciences, and more. The work is consistent across all of them: software that performs, costs less to run, and stays out of the user's way.
Thomas is writing a comprehensive practitioner's guide to Event Sourcing and CQRS, running to more than 400 pages across 18 chapters. It is built on a production-grade .NET reference implementation with four interchangeable event store backends, which is where every pattern in the book was proven before it was written about.
“Any software created and running either in MS-DOS, Windows, on a mobile device, or in the cloud, should be easy to use, performant, reliable, and be replaceable. It should not matter how old or new the software is. It's all about the end-user. Legacy applications are successful because they made it this far and fulfill a purpose. Treat them accordingly on the importance and purpose they serve.”
THOMAS JAEGER
40+ years of software, in one timeline
1984 · The beginning
Thomas Jaeger writes his first program on an 8-bit Z80 Amstrad CPC 464, igniting a passion for software development.
1988 · IBM-compatible 80386-DX
Thomas takes all his savings and purchases an IBM-compatible 32-bit 80386-DX computer with only MS-DOS 3.30. Over the coming years he teaches himself MS-DOS, GW-BASIC, QuickBasic, BASIC PDS 7, Turbo Pascal, C, Visual Basic for DOS, and assembly (MASM) using only manuals, books, and magazines.
1990 · First shareware program
Thomas creates his first successful shareware program, ACZAR for DOS, written in Visual Basic for DOS. It's an archive utility for zip, arc, lzh, pak, and related files. Competitors Arcmaster and Shez were hard to use; ACZAR had an intuitive interface and became very popular."If you've ever tripped over commands or felt lost working with archiving programs, ACZAR unravels the mystery and lets you get to work fast." Shareware Magazine, July-August 1993.
1991 · First professional programming job
Thomas begins his professional career in the real estate industry: residential property management at Real Estate Software Company, working on the MS-DOS flagship RPM which managed over 1 million properties, under the guidance of NARPM founder Ralph Tutor. He programs across IBM XT 8086, 80286, and 80386 hardware (MS-DOS 3.30 through 5.0, Windows 3.0, and Windows 3.1) using QuickBasic 4, Visual Basic for DOS, BASIC PDS 7, Visual Basic for Windows, MASM, and Delphi 1.0 / 2.0.
2025 · Founding Legacy to Modern LLC
To modernize legacy systems, Thomas establishes Legacy to Modern LLC, focused on practical software modernization using virtualization, Domain-Driven Design, CQRS, Event Sourcing, and AI / Machine Learning where it earns its place.
Industries served
Defense, financial services, healthcare, manufacturing, retail, professional sports, government, transportation, and more: 14 vertical markets across a four-decade career. From an Amstrad CPC 464 in 1984 to running a Bulletin Board System in 1994, to founding Legacy to Modern LLC and shipping modernization engagements on modern .NET, Go, and modern Delphi today.
What we stand for
Leadership in modern architectures
Thomas Jaeger has worked extensively with Domain-Driven Design (DDD), Command Query Responsibility Segregation (CQRS), and Event Sourcing. Applied carefully, these architectures help businesses scale and adapt while keeping systems robust and maintainable.
Our mission: simplifying software
At the heart of Thomas Jaeger's work is a commitment to demystifying software for users. The goal is intuitive design and user-centric solutions: technology that serves people, not the other way around. Software should be powerful, accessible, and easy to use.
Experience across industries
Over 40 years of experience across 14 industries, including banking, healthcare, and automotive. The throughline: software that performs, costs less to run, and stays maintainable.
40+ years building software
Thomas Jaeger, the founder, has been writing software for over four decades. He started in 1984 on an Amstrad CPC 464 and has since worked across 14 industries, including wealth management, electronic payments, and aviation. His work in Domain-Driven Design (DDD), Command Query Responsibility Segregation (CQRS), and Event Sourcing has helped small-to-medium enterprises, manufacturers, and government agencies improve efficiency and reduce operational cost. The mission of Legacy to Modern is the same one he has held throughout his career: build software that fits the work and serves the people who use it.
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