One of the rare completed progression series (though there will likely be follow up series too).
There's also a short story collection: https://www.amazon.com/gp/product/B00Z92K3PG (not free though)
And, the first audiobook is completely free for 3 months, whether you are a member or not.
For people too lazy to click through and double check on the books:
21 novels and a short story collection - the traveler's gate chronicles is free too
That includes 11/12 books of Cradle ( https://www.amazon.com/dp/B0753FP6SP?binding=kindle_edition&ref=dbs_dp_rwt_sb_pc_tukn )
Elder Empire (two trilogies that run in parallel - https://www.amazon.com/dp/B074C78XPJ?binding=kindle_edition&ref_=ast_author_bsi and https://www.amazon.com/dp/B074CCVM2J?binding=kindle_edition&ref_=ast_author_bsi )
Travelers Gate (Trilogy https://www.amazon.com/dp/B074CCBXYZ?binding=kindle_edition&ref_=ast_author_bsi and Short Story Anthology https://www.amazon.com/Travelers-Gate-Chronicles-Complete-Trilogy-ebook/dp/B00Z92K3PG?ref_=ast_author_dp )
And his newest book The Captain - https://www.amazon.com/Captain-Last-Horizon-Book-ebook/dp/B0BXPYQD4D?ref_=ast_author_dp