In this evaluation study, we investigated the extent to which Solitaired.com's online game, Solitaire, could be used to model players' performance on several validated cognitive tests commonly associated with mental acuity (i.e., memory and processing speed). Prior research found that Solitaire gameplay is affected by mild cognitive impairment and presumably closely related to mental acuity. Thus, we investigated the relationship between measures of mental acuity and Solitaire gameplay on Solitaired.com. Gameplay and self-reported data from players who opted into the evaluation were used to model players' performance on three brief online tests: (a) Choice reaction time, which involves processing speed, response selection/inhibition, and attention (n = 555, R[superscript 2] = 0.53); (b) Digit symbol matching reaction time, which involves processing speed and visual short-term memory (n = 707, R[superscript 2] = 0.54); and (c) Flicker change detection, which involves visual search, change detection, and visual working memory (n = 568, R[superscript 2] = 0.49). The important gameplay variables were mean time per move and use of hints, and the important player background variable was self-reported age. A major implication is how to report the model output information to players. As an engaging game, Solitaire can sustain motivation and elicit many important cognitive processes. Making full use of the information carried in players' interactions in online games--especially those games with a global audience--may provide new opportunities for exploring novel ways to measure cognitive processes in an aging population and, ultimately, to help players better understand their own gameplay performance. [This report was prepared collaboratively across the teams at Lyons Assessment Consulting and UCLA CRESST. This research is supported with funding from Unwind Media, LLC.]