Trelby is a screen writing software you can read more about on trelby.org.
Since its devs have not released an updated official version (from 2.2 to 2.3), we cannot use the available packages from the official site on the latest linuxes. Thus we need to compile the source. This is a quick and dirty way to do it, it worked for me, may not work for you. I will not give support if you run into problems. See referenced original post on google groups, which I have updated here.