This isn't exactly "can't live without," that would be HomeAssistant. But what I Immediately thought of?

Beyond All Reason

This is an RTS game in the spirit of Total Annihilation.

• labor of love
• fully 3d, including ability to rotate or raise/lower view
• tens of thousands of units without hardware lag for reasonably modem hardware (3-4 years old)
• all shots actively rendered, leading to:
• realistic friendly fire
• even air units can get hit by ballistic shots targeting land units (although odds are fairly slim)
• redirect-unit-to-dodge micro is effective in some situations
• meaningful terrain
• radar will have blind spots based on line-of-sight
• radar gives clear indicator of coverage during placement
• two factions, almost 200 units each, with tier 1, 2, and 3 units. A third (currently playable with a setting change) faction is in the works.
• crafty, non-cheating ai opponents
• free server hosting (!)
• active servers all times of day

The overall feel and balance of the game is great. The changes they make to balance are generally light and reasonable, and the game had a good community.

Fam and friends play together often.