Marin Sabo

Open to student jobs & 2027 internships · Remote or Osijek

I build software for systems that can’t afford to stop.

Mainframe Developer z/OS COBOL CICS Db2

Portrait of Marin Sabo

Hi, I’m Marin, a mainframe developer and CS student at FERIT Osijek. At CROZ I owned the Db2 database behind a z/OS application built in COBOL and CICS.

See my work Email me
  • CROZ Mainframe developer intern, 2026
  • 10 IBM mainframe badges, incl. Z Xplore All Star
  • Top 4 of the mainframe course, picked for QED 2026
  • 9 things shipped since 2023

01 — Featured work

DartZ on z/OS

A darts tournament and league system, built by our team during my internship at CROZ. CICS runs the transactions and screens, COBOL holds the business logic, Db2 stores the players, matches and leagues, and JCL handles builds and batch work.

Where
CROZ, Zagreb · team project
When
Jul – Sep 2026
Stack
z/OS · COBOL · CICS · Db2 · JCL

My role

  1. Designed and built the entire Db2 data model. Every program in the application read from and wrote to it.
  2. Test data for the whole team. I created the data the developers used to test their programs.
  3. Db2 & z/OS admin. I kept the database consistent and maintained the environment the team worked in.
CICS · TRANSACTION DZ01 3270 
DZL010                     D A R T Z                    OCT 2026
                        LEAGUE STANDINGS                        

 LEAGUE . : SLAVONIA AUTUMN LEAGUE 2026          ROUND 09 OF 14

 POS  PLAYER              P   W   L   LEGS    +/-    AVG   PTS
 ---  ------------------  --  --  --  -----   ---  -----   ---
   1  KOVAC, LUKA          9   8   1  48-21   +27  81.36    16
   2  MATIC, ANA           9   7   2  45-26   +19  78.02    14
   3  BABIC, TOMISLAV      9   6   3  41-30   +11  74.55    12
   4  JURIC, PETRA         9   5   4  38-34    +4  72.90    10
   5  NOVAK, DARIO         9   4   5  35-37    -2  70.13     8
   6  PAVLOVIC, IVA        9   2   7  27-43   -16  66.48     4




 DZL011I 6 PLAYERS LISTED. STANDINGS AS OF ROUND 09.

A recreation for this site. Names and numbers are made up. Swipe the screen sideways to see every column.

Modernisation

From datasets to Git

After DartZ was finished, we changed how it’s built and delivered, following IBM Dependency Based Build. The source of truth moved off the mainframe into Git, and a pipeline now delivers every committed change to z/OS automatically.

  1. VS CodeCOBOL, JCL and copybooks edited locally
  2. GitSingle source of truth, where every change is a commit
  3. PipelineStarts automatically on each push
  4. IBM DBBBuilds the programs affected by the change
  5. Zowe → z/OSChanges land on the mainframe

02 — Experience

Where I’ve delivered

Three very different jobs. In each one, people relied on me to get things right, and to fix problems fast.

  1. 07 – 09/2026

    Mainframe Developer (Intern) · CROZ, Zagreb

    Owned the database the whole team built on. z/OSCOBOLPL/ICICSDb2DBB
    • Developed an application on IBM z/OS as part of a team, using COBOL, PL/I and JCL with CICS transactions and a Db2 database.
    • As the team’s Db2 and system administrator, maintained the database and z/OS environment the entire development team depended on.
    • Contributed to the DevOps modernisation: moved the source of truth from the mainframe to Git, with automated delivery from the repository to the mainframe (IBM DBB, Zowe).
  2. 3 seasons

    Campsite Controller & Operations Support · Maistra d.d.

    Fixed billing problems live, in peak season. OperationsReservationsBilling
    • Resolved reservation and billing issues in real time during peak tourist season.
    • Worked daily with internal reservation and billing systems, where every error directly affects revenue and guest experience.
    • Rehired for three consecutive seasons.
  3. 5+ clients

    Freelance Web Developer · Self-employed

    Took client projects from first call to launch, on my own. HTML/CSS/JSWordPressFigma
    • Delivered custom websites (HTML, CSS, JavaScript, WordPress) from needs analysis to launch.
    • Ran each project on my own: negotiation, requirements and delivery within agreed deadlines.
    • Selected work is below.

Mainframe

  • z/OS
  • COBOL
  • PL/I
  • JCL
  • CICS
  • Db2
  • IBM DBB
  • Zowe

Programming

  • C
  • C#
  • SQL
  • JavaScript
  • Git

Web & design

  • HTML
  • CSS
  • WordPress
  • Figma

Languages

  • Croatian (native)
  • English

03 — Certifications

10 IBM mainframe badges

From hands-on z/OS challenges to hardware, security and build tooling. Every badge is verifiable on Credly.

IBM Z Xplore

  • ALLAll Star
  • ADVAdvanced
  • CONConcepts

IBM Mainframe Specialist · Interskill

  • z17IBM Z Hardware z17 — Foundations
  • ENVMainframe Environment — Foundations 3.1
  • SYSParallel Sysplex — Foundations
  • SECMainframe Security — Foundations
  • DBDatabase — Fundamentals 2023
  • APPApplication Programmer — Secure Coding

Build & security

  • DBBIBM Dependency Based Build Fundamentals
  • THMTryHackMe — ongoing cybersecurity training

Verify on Credly

04 — Other work

Web, design & research

Alongside mainframe, I’ve run web projects for clients on my own, from the first call to launch, and led a UX research project. That’s where I learned to work out what people actually need, and to deliver it on time.

  1. 01 Brushy A concept app that turns tooth brushing into a game for children. I did the research with 70 pupils and designed it in Figma. Research & UX · DentOS
  2. 02 Vukovarski Golubići Rebuilt a children’s choir’s outdated website on WordPress, then trained the staff to run it. Website redesign
  3. 03 GameChanger Website for a gaming and Web3 conference: 100+ speakers and sponsors, on a fixed launch deadline. Event website
  4. 04 WaveLance Landing page for a LinkedIn personal-branding agency, with a clear path to booking a call. Landing page
  5. 05 CodeHustling A central hub for a web-development community on Instagram. Community website
  6. 06 Ikarus Agency Brand identity and website for the web development agency I ran with a friend. Own agency · brand & website

What clients said

Marin is an outstanding web developer with excellent skills in both front end and back end technologies. His work is always user friendly, visually appealing, and high performing.

Additionally, he is a great team player, communicates well, and consistently brings a positive attitude.

I highly recommend him for any web development role.

Afreen Dharar Founder, WaveLance · client

Our old website made the choir look inactive. Marin built us a new one from scratch and trained us to run it ourselves, and we’ve been publishing news and galleries on our own ever since.

Dubravka Lemac Choir director, Vukovarski Golubići · client

Information about our community was scattered everywhere. Marin brought it together in one website and kept it running after launch. I’d recommend him for any web project.

Fabion Kallaku Founder, CodeHustling · client

05 — Shipped log

things shipped since 2023. Every launch gets a line here, no matter how small.

  1. Latest: DartZ delivery pipeline (09.2026), DartZ on z/OS (08.2026), IBM Z Xplore All Star (06.2026).

06 — Education

Education & recognition

Education

  • 2024 – now FERIT Osijek BSc in Computer Science · Software Engineering track · 3rd yearBachelor’s thesis, in progress: Applying DevOps Principles to Building a Db2 Database
  • 2020 – 2024 Technical School Požega Computer Science

Achievements

  • QED 2026, CROZ’s conference in Zadar: selected by the professor among the top 4 students of the elective course Fundamentals of Mainframe Technology to attend (grade 5/5)
  • Top national exam result in my class at Technical School Požega
  • Top 2% of students in Požega-Slavonia County
  • City of Požega Scholarship for academic excellence
  • 2nd place at the national competition “Opisujemo sustave” (2024), with maximum points for presentation
  • City of Požega Youth Council member (2022 – 2023)

07 — Contact

Let’s talk.

I’m looking for a student job or a 2027 internship in mainframe or enterprise development. I can work remotely, or on-site in Osijek.

marin.sabo.contact@gmail.com