All Tivos come with text2osd, but the output from that program leaves a lot to be desired. For that reason, the addon scripts look for out2osd and newtext2osd before dropping back to use text2osd. Out2osd comes with ncid and works well, although some of the colors seem a little washed-out on my TV. Newtext2osd hasn't been supported for a long time, but also looks good. Whichever one you use, make sure it's available on the path; otherwise, the addons won't be able to find it.
Out2osd and newtext2osd (I think) also support truetype fonts, but I'm not using those for the simple reason that it's murder to line up columns.