angesagt
popular / trendy
Colloquial for modern, popular, or fashionable.
Dieses Restaurant ist zurzeit in der ganzen Stadt total angesagt.
This restaurant is really popular all over the city right now.

popular / called for
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popular / trendy
Colloquial for modern, popular, or fashionable.
Dieses Restaurant ist zurzeit in der ganzen Stadt total angesagt.
This restaurant is really popular all over the city right now.

'Angesagt' is the past participle of the verb 'ansagen' (to announce). The basic idea of 'announcing' helps with understanding: something is so popular that it is being 'angesagt' (announced) everywhere, or an action is 'angesagt' (called for) by the situation as necessary.
Momentan sind kurze Videos in sozialen Netzwerken besonders angesagt.
At the moment, short videos on social networks are especially popular.
In the meaning 'popular' or 'fashionable', 'angesagt' is typical of colloquial language. It is often used to talk about current trends in clothing, music, places, or activities.
Welche Musik ist bei euch gerade angesagt?
What music is popular where you are right now?
When something is 'required', 'angesagt' often appears in fixed expressions. Typical examples are 'Vorsicht ist angesagt' (caution is called for), 'Eile ist angesagt' (haste is called for), or 'Zusammenarbeit ist angesagt' (cooperation is called for).
Bei diesem Projekt ist Teamarbeit angesagt.
In this project, teamwork is called for.
You can often recognize the meaning from the subject of the sentence. If it is a trend, a place, or a product, it means 'popular'. If it is a behavior such as caution or patience, it means 'required' or 'called for'.
Diese Bar in der Innenstadt ist sehr angesagt.
This bar downtown is very popular.
in
'in' and 'angesagt' can both mean that something is modern or popular. This use of 'in' is colloquial and is not the preposition as in 'in der Schule' (at school). 'Angesagt' is a normal adjective for something that is currently popular. Learners can easily confuse the words because 'in' very often appears as a preposition. But when it is used with 'sein', for example 'Das ist in' (That's in), it often means 'modern' or 'popular'.

Vintage-Möbel sind bei vielen jungen Leuten gerade sehr angesagt.
Vintage furniture is very popular with many young people right now.
Diese Jacken sind im Moment wieder in.
These jackets are back in right now.