Pasjans Solitaire might be a bit more popular than Solitaire.gg. We know about 1 link to it since March 2021 and only 1 link to Solitaire.gg. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
There are literally hundreds of different solitaire games, as can be seen here. Source: over 2 years ago
Have you looked at Pasjans? I don't know if you care about proprietary, but I don't know whether or not it is FOSS. Source: over 2 years ago
PySolFC - PySolFC is a collection of more than 1000 solitaire card games. It is a fork of PySol Solitaire.
World of Solitaire - Over 50 beautiful free web based Solitaire games. Klondike, Spider, FreeCell and more.
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NetSolitaire - Play Klondike, FreeCell, Spider and many other solitaire games online for free in your desktop or tablet browser
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BVS Solitaire Collection - Award winning collection of solitaire card games for Windows/macOS and iPad/iPhone.