Brightest stars of open source

Leonidas encourages its employees to participate in open source code projects and provides pay for development work performed in the employees’ free time. Find out more about our projects and utilise our expertise or make your own contribution!

Read Johanna’s blog entry on the subject: Why Open Source?

We are on GitHub

You can see our many public repositories on GitHub.

We are on Stack Overflow

We are contributing at Stack Overflow.

Projects we contribute to


Oppia is an online learning tool that enables anyone to easily create and share interactive activities (called ‘explorations’). These activities simulate a one-on-one conversation with a tutor, making it possible for students to learn by doing and get feedback.


An embeddable e-ticket system for events selling electronic tickets in PDF format. Used by Desucon, Tracon and other events to an annual total of over 300 000 € in tickets delivered.


In the early 00’s, Jussi Lahdenniemi made Tappio (“loss” in Finnish), a simple freeware double ledger bookkeeping application for Windows. Tailored for the Finnish financial legislation, it quickly became ubiquitous among student clubs and other small associations. Voitto (“profit” in Finnish) is a small collection of Python scripts that operate on the Tappio file format, implementing features crucial to everyday use of Tappio but not included in the original application.


Enables cosplayers and photographers to sign up for and organize cosplay photoshoots at conventions.


A point-of-sale and merchant sign-up system for second-hand sales at conventions and other events.


Passport authentication strategy against LDAP / AD server.

Embedded to machine learning

Personal blog of Risto Hietala, where I am documenting steps to build a temperature sensor network with Raspberry Pi devices, and eventually analyze the data with machine learning.


Drag-and-drop sortable grid view for React Native.


The Kompassi Event Management System is a comprehensive solution for volunteer-run conventions. It is used by Tracon, Desucon and dozens of other events to manage their workforce of hundreds of volunteers. There are over 4 000 registered users in Kompassi and e-ticket orders delivered through its e-ticket total more than 0.5 M€


Logs all requests to command line console (stdout) and responds 200 OK.

Useful for quickly viewing what kind of requests your app is sending.


Born out of frustration for existing self-hosted picture gallery software, the aim of the Edegal project is to provide the best and fastest self-hosted web picture gallery. With a strong focus on performance and user experience, the frontend is now undergoing a full rewrite in React & Redux. When ready, Edegal will replace a decade-old installation of Coppermine Picture Gallery hosting hundreds of categories, thousands of albums, tens of thousands of pictures and over half a terabyte of image data.