Old English has several glyphs that are obsolete today: For example þ, replaced by "th".
Old Japanese had several kana not used today, for example ゑ.
However, how about German? Did German used to have anything other than a-z, Umlaute, and ß?
German Language Stack Exchange is a bilingual question and answer site for speakers of all levels who want to share and increase their knowledge of the German language. It's 100% free, no registration required.Sign up to join this community
In all the following cases, it’s up to you what you consider a separate letter:
The long s (ſ) was a variant of the letter s with orthographic rules where to use it. In an extreme (contrived) example, its use could affect the meaning of the word:
The r rotunda (ꝛ) was a variant of the letter used after certain letters. The rules for typesetting affecting it were mostly typographical (based on position) and not orthographical (based on content). It survived longest in the abbrevation ꝛc. (etc.).
All the umlauts were preceded by variants where a small e was placed above the vowel, e.g., aͤ.
In very early prints, you had further similar combinations, in particular uͦ (u with a small o above; similar to ů).
Distinguishing between i and j is a rather new thing. Thus, from some point of view, a letter comprising i and j is gone. Similarly, u, v, and w all originate from the same letter.
In older handwriting it was common to use a macron accent over a single m or n to indicate doubling, e.g. writing Don̄erstim̄e instead of Donnerstimme.
Before moveable type, there was a plethora of shorthands and abbreviatures merging several letters or even entire words into one symbol.
Here is an example for Cases 2–5:
The only one I can think of: in older German scripts like Fraktur or Sütterlin there was an alternative form of the letter s, the "long s", see for example https://de.wiktionary.org/wiki/%C5%BF (in German.)
In German Fraktur typesetting, there were five ligatures that behaved as single glyphs: ch, ck, ſt, ſz, and tz. When letterspacing was increased, these ligatures stayed glued together as single glyphs. Increased letterspacing was relatively common. It was the usual method for highlighting words, much as italics or boldface is in Roman type. A word like „ſchwitzen“, for instance, would look like „ ſ ch w i tz e n “ when letterspacing was increased.
The Fraktur ligature glyph ſz was carried over to Roman type in the 1876/1901 German spelling reform. This is how the modern Roman type letter Eszett ß originated – it was not used in Roman type before the 1876/1901 spelling reform. The other four Fraktur ligature glyphs ch, ck, ſt, and tz were not carried over to Roman type. Therefore, they can be considered obsolete old German letters.
There is another which became Ö: Œ œ -> Ö ö
As @TilmanSchmidt and @mach stated the "long s" comes from Fraktur. It was used to set apart an "s" in the middle of a syllable from one at the end. This way one could distinguish i.e. between "kreischen" ("krei-schen", to scream) and "Kreischen" ("Kreis-chen", circlet).
Where these two came together within the same syllable they where replaced by a "ß", basically a ligature consisting of a "long s" (looks like a "f" without the horizontal line) and a "letter s".
This is the rationale behind the original set of rules covering the use of "ß" (the "Adelungsche Regel"). One writes "ss" in a "Silbengelenk" (also known as "ambisyllabischer Konsonant") , but "ß" otherwise: "Wasser" but "wäßrig", "müssen" but "muß".
(Notice, though, that "Silbengelenk" is a term coined by Peter Eisenberg, a modern german linguist, Adelung himself gave different rules but they lead effectively to the same result.)