What are your 'hidden gems' of accommodation platforms?

Let's pool our collective knowledge of accommodation booking options!

I've found there's a kind of gradation on booking options and platforms from the all encompassing Airbnb or booking at the top, slowly filtering down to platforms which offer more location specific options (think country or region) or other particulars (like serviced apartments only, or only places with co-work access). Here's a brief run down of what I think that gradation looks like, with some examples....

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Tier 1: Book anything, anywhere (Airbnb, booking.com, hostelworld, VRBO)
Tier 2: Slightly tighter geographic remit or country/region specific focus (Agoda, Selina, idealista, hello landing)
Tier 3: Even tighter geographic remit / much lesser known platforms (Flatio.com)

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My question for the community...
**Are you using or aware of any platforms in the 'Tier 3' category? **
What are they? What's their geographic focus?
Why do you like them over Tier 2/1 options?

Hoping to expand options for everyone here... let us know what you are using!

Cheers,