No, there isn’t a single nationwide application portal like UCAS. Most international students apply either through uni-assist, which is a central admissions service used by many universities to evaluate international certificates and forward applications, or directly to the university if it does not use uni-assist. For programmes with nationwide admission restrictions (such as medicine, pharmacy or dentistry), applications are handled via Hochschulstart.de. The DAAD course finder and individual university “How to apply” pages tell you which route to follow for your chosen programme.