Which e-commerce trend has most significantly changed how mathematical software products are sold in the last decade?

The online marketplace for mathematical tools, educational resources, and software has transformed how students and professionals access mathematical products. This trivia question explores an interesting trend in how mathematical products are marketed and sold online, reflecting changes in customer shopping habits and e-commerce strategies. Test your knowledge of the intersection between mathematics education commerce and digital retail!

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Subscription-based models replacing one-time purchases (e.g., MATLAB, Mathematica, and other computational tools moving to monthly/annual subscriptions)
NFT certification of mathematical proofs bundled with software purchases
Mandatory in-person activation of all advanced mathematical software for security reasons
Single-use license keys that expire after solving a certain number of equations