Danielius Zajenčkauskas — Product Engineer

Product Engineer

I'm a full-stack engineer with a front-end focus, building complex products from interface to infrastructure.

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35: enterprise applications
12: shared platform packages
5: marketplace applications
7: selected case studies

Selected work

Complex products, clearly engineered.

A website for a bespoke-crate workshop, built around a 3D crate that comes apart as you scroll.

01/ 05

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2026 · case1.co.uk

CASE1

A website for a bespoke-crate workshop, built around a 3D crate that comes apart as you scroll.

Modelling in code — Modelled every board, batten, countersunk screw and foam block on Three.js geometry from one dimension spec, plus a lathe-turned porcelain vase. All textures are generated rather than photographed: wood grain with growth rings, knots and end grain, layered ply edges, CASE1 stencils and a crackled glaze.
Scroll story — Turned the model into a pinned five-step story that reassembles when you scroll back. Frames render only while something moves, and the stage warms toward the brand pink with each step so progress still reads on a phone.

Next.js 16React 19TypeScriptReact Three FiberThree.jsPrivate source

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2024 · Private commercial platform

Lobasoft Enterprise Platform

A 35-app enterprise platform for ERP, financials, payroll, HR and audit workflows.

Scope — As the sole front-end engineer, I own delivery from established OData/REST contracts to production workflows across accounting, payroll, HR and audit.
Platform foundation — Built and maintain 12 shared packages and a config-driven resource layer that produces consistent forms, tables, filters, actions and detail views across 35 applications.

React 18TypeScriptMaterial UIReact PDFReact EmailPrivate source

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2024 · deliver1.co.uk

Deliver1

An international-removals platform with instant quotes and multi-step booking across road, sea and air.

Customer journey — Rebuilt the customer-facing Next.js architecture and developed instant-quote, inventory and multi-step booking journeys with step-specific validation.
Backend, payments and verification — Extended Strapi with issue/update models, public and internal endpoints and tracking tokens, and integrated Stripe deposits and Firebase phone verification behind server-owned routes with explicit retry and failure states.

Next.js 15 / 16React 18 / 19TypeScriptStrapiMaterial UIPrivate source

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2026 · toolkit.zajenckauskas.lt

Toolkit

An open-source hub of 49 privacy-conscious browser tools for image, text, developer, design, PDF and accessibility work.

Architecture — Designed a Turborepo workspace that separates the Next.js shell, design system, framework-independent tool logic and registry.
Tool catalogue — Implemented the tool catalogue on Canvas, Web Crypto, fflate, markdown-it and QR generation, keeping conversion, parsing and file-processing logic outside React so it's directly testable.

Next.js 15React 19TypeScriptTurborepoEmotionOpen source

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2025 · muses.lt

Musės — Fly Tying Market

A specialist fly-tying marketplace connecting a customer storefront with seller, support and administration workflows.

Marketplace foundation — Architected five applications—a storefront, seller, support and administration workspaces plus a Strapi 5 API—and six packages for shared domain and UI concerns.
Transactional integrity — Built Stripe and inventory services so a retried payment or a webhook delivered twice can never double-charge a customer or double-count stock, and modelled seller wallets as a running transaction history with payout, statement, reconciliation and dispute workflows.

Next.js 16React 19TypeScriptNode.jsStrapi 5Private source

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Available for selected work

Building or improving a digital product?

I work with product teams, startups and agencies on React products, integrations and existing platforms.

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Product Development

React and Next.js products supported by the APIs, integrations and delivery systems they need.

New productsMVPsNew featuresSaaS

Existing Product Support

Join an existing codebase to ship features, fix front-end problems or improve architecture.

Feature developmentRefactoringPerformanceIntegrations

Agency Development Partner

Additional front-end or full-stack product capacity for client work and busy internal teams.

Figma → ReactClient projectsIntegrationsWhite-label development

About

Making complicated work feel simple.

If a complex workflow cannot be explained clearly, I do not consider the interface finished.

What I build

Front-end engineer with nearly five years of experience across enterprise ERP, finance, payroll, HR, e-commerce, healthcare and real estate products. I specialise in React architecture and complex product interfaces, and I also build the Node.js/Strapi services and integrations needed to deliver complete products.

How I build

My current work ranges from shared packages used by 35 enterprise applications to an independently built five-application marketplace. I work with REST and GraphQL APIs, PostgreSQL, payments, PDF generation, transactional email and production delivery, backed by focused automated tests.

What shapes the work

A graphic design background shapes how I approach information hierarchy, responsive behaviour and interaction detail. I prefer pragmatic systems that are clear to use and straightforward to maintain.

Engineering capabilities

How I approach the work.

The tools change; the priorities do not: clear workflows, sound architecture and reliable delivery.

Product Engineering

Turning domain rules and user needs into clear, maintainable product workflows.

Workflow DesignInformation ArchitectureResponsive UXConversion JourneysDomain ModellingProduct Delivery

Front-end Architecture

Building typed foundations that stay coherent across applications and teams.

TypeScriptReactNext.jsReact Hook FormYupRedux ToolkitZustandShared PackagesConfig-driven UIMonorepos

API & Data Orchestration

Coordinating data contracts, asynchronous states and recoverable integration flows.

Node.jsStrapiPostgreSQLREST APIsGraphQLSWRWebhooksType-safe Contracts

Performance & Accessibility

Keeping interfaces fast and usable across devices, content and assistive tech.

Semantic HTMLAccessibilityWeb PerformanceProgressive LoadingPayload ControlResponsive Delivery

Reliability & Quality

Making critical journeys testable, understandable and resilient when dependencies fail.

PlaywrightVitestReact Testing LibraryError HandlingCI/CDAI-assisted development

Content & Delivery Systems

Connecting editable content, documents, communication and production infrastructure.

NodemailerReact EmailStripeDockerPM2NGINXCloudflare Turnstile

Perspective

Fluent and curious beyond code.

Clear communication across teams, with interests that keep the work grounded and observant.

Communication

Languages

LithuanianNative
EnglishFluent

Outside the screen

Beyond Code

Visual ArtsMinimalismCookingFly fishing

Get in touch

Let’s build something useful and dependable.

Open to thoughtful product engineering work where quality and maintainability matter.

Start a conversationdanielius@zajenckauskas.lt