Pentarab
Pentarab
KOEN
Resume · Oct 2026

Rak Gyu (James) Song송락규

Software Engineer · Founder, Pentarab

I started at Samsung Electronics, debugging the Android platform on Galaxy devices and optimizing the ART runtime. At Spoqa I took on full-stack web and the production environment, and at eBay Korea (now Gmarket) I led the frontend modernization of a large seller platform. Pentarab, registered as a business in 2019, became my main work after parental leave; since May 2025 I have been building iOS, macOS and Android apps — and the release and operations infrastructure behind them — full-time and on my own.

LinkedInGitHubinfo@pentarab.com
Total experience
15 yrs 10 mos
Jan 2011 – present · incl. 1 yr parental leave
Employed
14 yrs 5 mos
Samsung Electronics · Spoqa · eBay Korea
Pentarab full-time
1 yr 6 mos
May 2025 – present · registered 2019

Durations count both the first and the last month, the way LinkedIn does. Leaving eBay Korea and going full-time at Pentarab fall in the same month, so that month is counted once in the total.

01Experience

2025 – Present
2025.05 – Present
1 yr 6 mos

PentarabOne-person software studio · registered 2019

Founder (full-time)

I plan, build and run productivity, camera, creative, wellness and AI apps for iOS, macOS and Android on my own. While at eBay Korea I built apps as a hobby on weekends and in the evenings; after parental leave I took it on seriously, and I have run it full-time since May 2025.

Operations
  • 20 iOS and 5 macOS apps on sale on the App Store and 150 apps on Google Play (Oct 2026) — the Android line is managed in a single Flutter monorepo
  • Every iOS and macOS app launched on Product Hunt at release; store metadata ships in 36 locales by default
AI · LLM
  • Coding-agent harness — domain agents, skills and memory kept in one repository, with the codebase indexed as an AST graph that agents query directly. Restructured after measuring seven weeks of session logs to find where the cost concentrated
  • In-house GPU generation pipeline — app icons, illustrations, store assets and game sprites generated internally with ComfyUI
  • In-app AI features — generative model calls wrapped in Cloudflare Workers to keep keys off the device, with StoreKit 2 receipt validation and daily limits enforced on the server
Infrastructure · Release
  • Go + React admin console — containers through the Docker Engine API, DNS through the Route53 API, and nginx and TLS certificates, all from one screen
  • Self-hosted GitHub Actions → GHCR → webhook redeploy pipeline; an in-house analytics system (Cloudflare Worker + D1, with iOS and Flutter SDKs)
  • Build uploads, metadata and review submissions automated through the App Store Connect API and the Google Play Developer API
2017 – 2025
2017.09 – 2025.05
7 yrs 9 mos
Includes parental leave, 2024.05.18 – 2025.05.17

eBay Koreanow Gmarket · Gangnam, Seoul

Senior Software Engineer

I stayed with the same organization after the 2021 acquisition by Shinsegae Group renamed the company Gmarket, and left when my parental leave ended. I led the frontend modernization of ESM Plus, the seller management platform used by Gmarket and Auction sellers.

  • Led the ESM Plus frontend renewal — moved .NET Framework 3.5 / Razor screens that had been in service for over ten years to a modern frontend architecture
  • Ran a Vue.js proof of concept, then chose a React / Next.js architecture and designed a phased migration of product registration, editing and management
  • Built the routing, state, authentication, session and API bridges for the hybrid Razor + React stage, so the move happened incrementally with no downtime
  • Designed and built Product Registration 2.0
  • Built an in-house design system and a page management scheme covering new domains and legacy pages together
  • Renewal development environment — service layer, page routing, debug mode, in-house build system and a shared project structure
2015 – 2017
2015.03 – 2017.08
2 yrs 6 mos

SpoqaSeoul

Software Engineer

I owned DodoMessage, an automated in-store messaging platform in Korea and Japan, from the backend to the production environment. It sent a welcome message over MMS or KakaoTalk right after a customer checked in, and offered condition-based campaigns such as birthdays and anniversaries, along with store reports.

  • Backend API servers and internal service integration; designed internal services on a microservice architecture
  • Admin and operations screens in React/Redux
  • Automated message delivery and asynchronous job processing with Celery
  • Built the Docker/AWS production environment and ran CI/CD on CircleCI

Python · Flask · PostgreSQL · SQLAlchemy · Celery · React · Redux · Docker · AWS · CircleCI

2011 – 2015
2011.01 – 2015.02
4 yrs 2 mos

Samsung ElectronicsSuwon

Assistant Engineer → Engineer

Android platform issues on Galaxy devices and the performance of the Android Runtime (ART).

Engineer2014.03 – 2015.02
  • ART performance analysis and optimization; analysis of the compiler architecture
  • Analysis and debugging of problems arising in the ART runtime and during compilation
Assistant Engineer2011.01 – 2014.03
  • System issue analysis and incident response for flagship devices including the Galaxy S3, S4, S5 and Note 3
  • Android kernel- and framework-level debugging, performance analysis, and root-cause analysis and fixes for memory leaks
  • Source code management (SCM) and branch operations for many Galaxy models; Python automation tools
2010 – 2011
2010.01 – 2011.01
1 yr 1 mo
Internship-like program · not counted in the total

Samsung Software Membership, 20th cohortGangnam

Software Engineer

Computer vision and image processing in Samsung Electronics’ software talent program.

  • Automatic correction for projection onto curved surfaces — drove an industrial camera at the register level to sync pattern projection with the shutter; a redesigned scan mode raised throughput about 14×
  • DICOM CAD viewer — a project with Samsung Electronics’ HME division, with SVM classification and similar-case retrieval
  • Panorama stitching — SIFT, k-d tree and RANSAC implemented from scratch in C++/OpenCV
  • Dangjang Manna — an Android app that polls a group for availability and settles a meetup time (developer on a team of four)

02What I build at Pentarab

20
iOS apps on the App Store
5
macOS apps on the App Store
150
apps on Google Play
36
default store locales

App Store and Google Play figures as of October 2026.

Selected products
Pro2CameraiOS
Manual & RAW camera, Metal filters
ConstellaiOS
Fortune readings · iOS & Android
NovelDeskmacOS
Long-form writing desk · Tauri + React
KorioiOS
Korean & TOPIK learning
LogoFormiOS
1,860 templates by industry
ArtooniOS
AI photo transformation
CalmnestiOS
Breathing & sleep · Live Activity
FocusMindiOS
Focus timer · iOS & macOS
PulseiOS
Video effects camera
WobbleiOS
Metal mesh physics toy
AsoPilotmacOS
ASO research · macOS
AppBoardmacOS
App Store Connect metadata · macOS

The harness, shared modules and release setup are written up on the engineering page. How it’s built →

03Skills

Mobile
SwiftSwiftUITuistStoreKit 2MetalWidgetKitFlutterDartAndroid
Web
TypeScriptReactNext.jsReduxVue.jsViteTailwind CSSTanStack Query
Backend
Go (go-chi)Python (Flask)PostgreSQLSQLiteMySQLCeleryCloudflare Workers
Infra
DockerNginxGitHub ActionsGHCRAWSFastlane
Desktop
SwiftUI + GRDBTauri 2 (Rust)C++ / MFC
AI · Systems
Claude Code harnessComfyUIOllamaApple Foundation ModelsOpenCVAndroid ART

04Awards · Publication · Projects

Awards
  • bada Global Developer Challenge — Special winner · Samsung Electronics · 2,077 teams from 54 countries2010.12
  • Samsung UX Create Program — Bronze · Samsung Electronics2010.09
  • T store App Contest — Bronze · SK Telecom2010.06
Publication
A music recommendation service built on lyric sentiment and audio features · Microsoftware magazine · 4-part series · 5 co-authors2010.10 – 2011.01
Projects · Exhibitions
  • DevRank2012–2014 — Developer ranking inspired by PageRank; graph analysis on Apache Giraph and Hadoop
  • BBQ/Pizza2012–2014 — Automated trading for Korean stocks — a C++ brokerage terminal client talking to a Python server over Thrift
  • Monoka2012–2014 — Collected community posts and comments and ranked them by how comments reacted
  • 2009 LIGHT WALL2009.08 — Ran the media façade on the outer wall of the Seoul Museum of Art; interviewed by Arirang TV
  • Vision Art Tool2009 — Real-time computer vision plug-in framework for media artists

The 2012–2014 side projects were hobby work with teammates.

05Education · Languages

  • Soongsil University, School of Media · B.S. · Computer Software and Media Applications2005 – 2011
  • Languages · Korean (native) · English (limited working proficiency)