Android Custom ROM's - Alternative Android Operating Systems

What are they? - Modified versions of Android that replace the manufacturer's original operating system.

Why use them? - Greater privacy, security, customisation, fewer Google services and extended device lifespan.

How are they different? - Standard Android: Google services and manufacturer software integrated.

Custom ROM: Greater user control; Google services may be optional or absent.

iOS: Apple-controlled operating system with limited system modification.

How popular are they? - A niche but established global community, with millions of installations across different ROMs.