To generate test cases for the "Accelerated Railgun" problem, we need to consider the constraints and inputs specified in the problem statement. Here is a Python function that generates random test cases within the given constraints:

```python
import random

def random_real(a, b, precision=6):
    """Generate a random real number between a and b with given precision."""
    return round(random.uniform(a, b), precision)

def tcgen():
    test_cases = []
    
    while True:
        # Generate a random D within the range (0, 50]
        D = random_real(0.0001, 50.0)
        
        # Generate random px, py within the range (0.0001, 0.9999]
        px = random_real(0.0001, 0.9999)
        py = random_real(0.0001, 0.9999)
        
        # Generate random vx, vy within the range (0.0001, 0.9999]
        vx = random_real(0.0001, 0.9999)
        vy = random_real(0.0001, 0.9999)
        
        # Create a dataset
        dataset = (D, px, py, vx, vy)
        
        # Append the dataset to test cases
        test_cases.append(dataset)
        
        # Randomly decide whether to add another test case or to end with D=0
        if random.choice([True, False]):
            # Generate another dataset
            continue
        else:
            # End the input with D=0
            test_cases.append((0,))
            break
    
    return test_cases

# Example usage:
test_cases = tcgen()
for case in test_cases:
    if case[0] == 0:
        print("0")
    else:
        D, px, py, vx, vy = case
        print(f"{D}\n{px} {py} {vx} {vy}")
```

### Explanation:
1. **Function `random_real(a, b, precision=6)`**:
   - Generates a random real number between `a` and `b` with a specified precision.
   
2. **Function `tcgen()`**:
   - Generates multiple test cases until a random decision is made to end the input with `D=0`.
   - For each test case:
     - It generates a random `D` within `(0.0001, 50.0]`.
     - It generates random values for `px`, `py`, `vx`, and `vy` within `(0.0001, 0.9999]`.
   - Randomly decides whether to continue adding test cases or to terminate the input by appending `(0,)`.

### Example Output:
This function prints the generated test cases in the required format. Each dataset consists of `D`, followed by `px`, `py`, `vx`, and `vy`. The last line will be `0` to indicate the end of input.

You can use this function to generate diverse test cases for the problem, ensuring that they adhere to the constraints specified.