The first two Apple II models (the ][ and ][+) were unable to display lower case on the text screen. Some 3rd parties made lower-case adapters that replaced the character ROM (e.g. Dan Paymar's popular device). The device from Lazer Systems (a/k/a Lazer MicroSystems) was called the "Lower Case Plus", pictured here. One of the interesting features was that you could use an EPROM programmer to replace the font with one of your own design. You could also add on a "Character Set Plus" to have additional ROM fonts.
Lazer Systems had another product called the "Graphics Plus", which allowed the font to be updated with software. The idea was that you could use text characters as graphics tiles and create games that ran much faster than similar code that used the hi-res screen (the text screen being 1/8th the size).
How did font selection and updating work?