[PC] [Late 90s/Early 2000s] 2D side-view defense game where you control a cannon on a castle wall and shoot alien spaceships coming from above

I've been trying to remember this game for a while. I already ran it through an AI and it couldn't figure it out either, so I'm lazily having it write this post for me.

**Platform:** PC

**Genre:** Arcade / Defense shooter

**Graphics:** Pixelated, 2D

**Estimated year:** Late 90s to early 2000s

**What I remember:**

- Side-view perspective, but the castle wall is a **horizontal strip at the bottom** of the screen

- You control a **cannon sitting on top of that wall** and can move it **left and right** along the wall

- You can also **aim the cannon up and down** to adjust the firing angle

- **Alien spaceships attack from above** (coming down from the sky)

- **Upgrades/powerups drop from the sky** and you have to collect them to improve your cannon

- The game could be played **solo or with a second player** (co-op)

- Pixel art style, pretty simple visually

- I'm fairly sure it was included on a **Bravo Screenfun CD** (German gaming magazine), so it was likely a freeware or shareware title

Any idea what this is?