I am a big fan of Free/Libre and Open Source Software. As a developer I very much value that it allows me to freely use and if necessary modify software written by others. Since I benefit so much from work people have made available under an open source license it seems only fair that I do the same.

I want everyone to be able to use my software, not only those who can pay for it. That’s why all of the open source software I create is available free of charge.

However, open source developers still need to make a living. So if you use one of my projects and can afford it, please consider becoming a sponsor. Donations currently allow me to work on open source full time đź’–

If you’re interested to learn how that whole “full-time open source developer” thing has worked out for me so far, check out these blog posts:

For a list of most of my open source contributions check out cketti on GitHub.


There are multiple options to financially support my open source development.


Liberapay is a recurring donations platform for free software projects. You can use a credit or debit card (Visa, MasterCard, American Express), a Euro bank account (SEPA Direct Debit), or a PayPal account to donate money to me. While the goal of Liberapay is to facilitate recurring donations, by selecting “manual renewal” you can also make one-time donations.

Donate using Liberapay

GitHub Sponsors

This is a convenient way for users of the development platform GitHub to financially support me with recurring or one-time donations.


If you don’t want to create a Liberapay account, you can give money using PayPal directly. Supports both one-time and monthly donations.

Bank transfer

For SEPA transfers use the following information:

IBAN: DE69 4306 0967 7017 5834 01
Name of benificiary: Christian Ketterer
Reference: Open Source Development

If you want to donate to the K-9 Mail project in particular, you can do so via K-9 Mail’s Liberapay page.