The Base Version

When I was 16, I had a Xiaomi Mi A1. This was my second-ever smartphone and my first Android phone, and I loved it. The customization options, the apps, the widgets... everything was so new and exciting to me. But one thing became increasingly clear: Every single day, I made the same four kinds of Google searches. "Pascals to PSI", "Die roll", "QR Code Generator", and "Time between Thursday 16:00 to Friday 13:30". Each time, I had to open the browser, type the query, open the site, and enter the data. It was five minutes per day tops — but I felt like I could build something better. So, after tons of tutorials and very, very bad Java code, I built centr — a multitool and my first Android app.

Unfortunately, I don't have the first version of centr anymore, but I do luckily have a changelog.txt file that I used to host on my website. I'll be referencing it in the post.

It was very simple — centr Beta 1.0, the first public release, had only the most essential applets for me:

• Conversions:
  • Distance
  • Mass
  • Volume
  • Temperature
• Finance:
  • Tip Calculator
• Chance:
  • Die Roll
  • Coin Toss
  • Random Number
  • Password Generator
• Others:
  • QR Code Scanner
  • QR Code Generator
  • Color Picker

I added some bug fixes in 1.1, 1.1.1, 1.1.2, 1.1.3... And then, in version 1.2, I added my new favorite applet:

The Time Remaining Calculator. I used this applet almost daily for my 3D printing projects. I had an Ender 3 at the time, and it only showed two stats for print jobs: Time elapsed, and completion percentage. This applet allowed me to enter those two values and get an estimate of the remaining time. It was super useful for planning my day around print jobs. I could, for example, see that my print had been running for five hours and that it was 60% complete, so I could expect it to finish in about 3:19.

A few weeks later, someone reached out via email asking for a feature for them to disable haptic feedback. It was small, but it felt so good to know that someone was using my app and cared enough to ask for a feature. I implemented this in version 1.2.1.

For version 1.3, I added two new features:

• An option to scan a QR code from the gallery instead of just the camera
• A switch button to quickly toggle between the two units being converted in the Conversions applet

Luckily, through the power of Git, I still have Beta 1.3's APK! Here's how it looked:

As you can see, the coin toss applet was anything butt classy.

In version 1.4, in February 2022, I added the Time Conversion applet, the Tax Calculator applet, and translated the app into Spanish.

Beta 2.0

With Beta 2, came several new features:

• A version check to notify users of new updates
• Area conversion applet
• Speed conversion applet
• Data conversion applet
• Data-rate conversion applet
• New units for Volume conversion
• Several bug fixes
• A new awful theme (I still cringe thinking about it)

The Release Version

In June of 2022, I finally released centr 3.0. It came with an awesome new theme system (if I do say so myself), accessibility improvements, a passphrase generator applet, a redesign of the QR Scanner applet, more settings, better permission request management, and a lot of bug fixes. I'm quite proud of this release, as it felt like the app had finally matured into something I could share with the world! Still no Play Store release, though — I was 17 at the time, and developer accounts require you to be 18 or older.

What's Next?

Sadly, after an unlucky incident with Respondus LockDown Browser breaking my Windows install, I lost the source code for centr. The latest version in the Play Store had some major bugs, so I just unlisted it and haven't updated it since. I've had re-writing it on my radar (especially a browser version), but I haven't found the time to do it yet. If I do end up re-writing it, I want to make it open source like the rest of my projects. If I do, I'll keep you posted.

Conclusion

centr started as a small, selfish tool to shave minutes off my daily routines, but it grew into a project that taught me a lot about product design, polish, and listening to users. Building tiny applets helped me practise shipping small, useful features and iterating on them based on real feedback. Even though it's simple, I'm proud of what centr became — a personal reminder that useful software doesn't need to be huge to matter.

Unfortunately, I don't have a download link for the app anymore, but if you want to see more of my code, check out my Git server at code.marvil.co↗!