For questions about conlangs that have features similar to European languages (either by design or by accident). Also for questions about the features that make conlangs similar to European languages.

European languages share some surprising features in common. A list of features constituting Standard Average European, a Sprachbund, is given in a portion of the 2001 book Language Typology and Language Universals written by Martin Haspelmath. The features are characterised by the following four criteria

  1. Most of the "core" European languages possess it.
  2. Nearby languages (Celtic, Turkic, etc.) lack it.
  3. Eastern Indo-European languages (Armenian, Iranian, Indic languages, etc.) lack it—this prevents us from merely calling it a feature of the Indo-European language family as a whole.
  4. It is not found in the majority of the world's languages.

A list of twelve features can be found in this answer.