Ideas which will covers all Basic Appian Features with good complexity - New To Appian.
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I would recommend you to Log in to Community via below link.It covers all topics with application development step by step based on skill and level.https://appian.com/landing/community-edition/get-started
Appian Tutorialshttps://docs.appian.com/suite/help/25.2/Tutorials.html
A few project ideas are attached that involve integrations. I would recommend you can either use dummy data from freely available APIs, or you can create data in Appian and expose it as a Web API, then consume the same data in your application using integrations.PDFPDFPDF
Here is a thread you can refer to find some usecases to start with!
Also, do checkout Appian tutorials in Appian Academy to follow along if you are new to Appian basic concepts!
Here's one of the POC which will cover almost every object in Appian while building the application