After short investigation I found only one Open Source application to prepare fonts - FontForge. They have very good manual which can lead you into the world of typography. They also link to very interesting Adam Twardoch's site about diacritic signs in Polish fonts. If you enjoy fonts, you will find the figures simply beautiful.
If you plan to make a new font, you will fence with a license problem. The first trace of license I could accept was SIL's OFL (Summer Institute of Linguistics' Open Font License). FSF states on their GNU licenses list, that the license requires a program to be distributed with the fon, even its a "Hello World" program. I read this license and I didn't find there anything like this (the license text is short and pretty simple), but I chose for my imaginary font (I created a half of letter 'C' :-)) GNU license with the recommended exception. I thought FSF mentioned OSF 1.0, but they are clear, that they are describing version 1.1.
Short PDF document about digitising of Polish font from 1960 - Antykwa Toruńska. Tree years to first pretty complete version, and another tree to complete the set with more faces then the original :-)
How to install fonts in Debian/Ubuntu.