The Loose Association of Wargamers

Crossfire I always thought would handle marines vs aliens and humans vs daleks or cybermen.

Pony wars when it returns also has a good colonial marines vs alien hordes vibe.

I do have an idea about using cards...

Here's that official Stargrunt 2 free download: https://shop.groundzerogames.co.uk/rules.html

Thanks for that. I see FUBAR actually have an Aliens draft... and Starship Troopers...

I reckon they're all you need for 'dipping a toe in the water' projects.
Good for introducing non-wargamers to a quick bash too.