15 Free Kindle books from Luke Chmilenko, books 1-3 of 5 different series. I think they're mostly in the LitRPG/Progression Fantasy vein:
Ascend Online - Early VRMMO LitRPG. I already had these, and have read and enjoyed book 1.
Book 1 UK:
https://www.amazon.co.uk/Ascend-Onli.../dp/B01M01ET8E
US:
https://www.amazon.com/Ascend-Online.../dp/B01M01ET8E
Starbreaker - I paid actual money (sure, only 0.99) for book 1 a few weeks ago, but haven't read it yet.
Book 1 UK:
https://www.amazon.co.uk/Starbreaker.../dp/B0DW7CGM5X
US:
https://www.amazon.com/Starbreaker-1.../dp/B0DW7CGM5X
Paragon - Co-authored with Alex Knight
Book 1 UK:
https://www.amazon.co.uk/dp/B09T3S5MGS
US:
https://www.amazon.com/dp/B09T3S5MGS
Immortal's Ascent
Book 1 UK:
https://www.amazon.co.uk/dp/B0DJPRJ3ZK
US:
https://www.amazon.com/dp/B0DJPRJ3ZK
Savage Dominion - Co-authored with G D Penman. Complete trilogy. - LAST DAY
Omnibus UK:
https://www.amazon.co.uk/dp/B0CZV39FZ7
US:
https://www.amazon.com/dp/B0CZV39FZ7
Note that
Savage Dominion is only free until the 3rd September, according to his website. The rest are free until the 7th.
Immortal's Ascent and
Starbreaker seem to be "downloadable in other formats."