Im Allgemeinen (In general)
Why do I see Allgemeinen capitalized most of the time? From what I can find the word is an adverb or adjective; I have not seen where it is a noun.
Adjectives and verbs can be written with capital letters. One reason that triggers the use of capitals are some words like "im" (in dem), "beim" (bei dem). However, there isn't a noun following to which this relates to.
Beim Spielen hat er sich verletzt. = He was playing when he got hurt.
Beim Malen spricht er mit seinem Freund. = He was drawing and talking to his friend.
Just think of "beim" as "bei dem" :) And actually, be it at the beginning or further in the sentence and not capitilised, it's the following, related word, that may originally not be a noun, (in the exemples given by Birgit, verbs) that kind of becomes one and thence gets the capital letter.
I'm not totally sure of that one, but as it is sort of a set expression, the rules may change a bit. Plus, German is familiar with making a adjective work as (sort of) a noun: I had the worst difficulties with "Erwachsene", for instance, as it is a substantive, but retain the properties of the adjective (litteraly "grown up") when it comes to declensions. I have to thank profusely the person who solved the mystery for me, now I see the same pattern from time to time for some words. So, perhaps we could think of "in Allgemeinen" as "as a generality"?
Native's opinion welcome :)
The rule is called "Substantivierung", you might want to check
for further examples.
In case you haven't noticed yet, Slam :-) Here an example:
Im Allgemeinen -> In dem Allgemeinen
Beim Malen -> Bei dem Malen
Ins Zimmer -> In das Zimmer
"in" and "bei" are prepositions which you can connect with its following article to make it shorter. But be careful! The female article "die" is an exception! "Beir" (Bei der....) and "ir" (In der....) do not exist^^
In the first months of my learning, these sites confused me to no end (too much information), but after that, they put me to a new level :)
I did use Linguee and I saw that Allgemeinen was both capitalized and not in the external sources (Externe Quellen). I should use Reverso more; it just is not one of my Bookmarks. I too used to be confused by these resources and became comfortable with Linguee; and in this case it did not help me much. Danke sehr.
Unfortunately there are a couple of fixed phrases in German where adjectives are used as nouns and hence are capitalized. I fear you have to learn these by hard. For example:
im Allgemeinen - in general im Großen und Ganzen - overall ins Schwarze treffen - to hit perfectly auf die Schnelle - quickly, in a hury in Kürze - shortly, (derived from kurz - short)