AgX is more recent than ACES and although not as contrasty, it has better color accuracy representation. ACES tends to shift red hues to orange and yellow at high intensities, but AgX maintains hues regardless. It also has a gentler ramp-up to highlights color desaturation for a more pleasing aesthetic. Right now AgX is present but dormant in the Oolite shaders. To activate it for your own testing, open oolite-final.fragment in the Shaders folder and change the line
#define OO_TONEMAPPER_AgX 0
to #define OO_TONEMAPPER_AgX 1
.And since we can't possibly talk tone mappers without images, here are some comparison shots. First is ACES followed by AgX Punchy.
Test Pattern:


In-game:














In the last shot you can see ACES shifting hue to yellow when very bright reds are shown. This is not the case with AgX.
This tone mapper is available for both Windows and Linux, as it is SDR-only.