It's quickly approaching a 1.0 release, and from what I hear when that happens it's going to see a price bump as well.
Re:OpenTTD 1.8.0-RC1
by AdamGibbins on Sunday April 01, 2018 @03:20AM
(#16727166)
By 10 USD on the 16th: https://www.factorio.com/blog/post/016-price-change
It has support for Windows, OSX and Linux.