Https://tabletopia.com/ seems to be a freemium platform for playing many (all?) commercial boardgames and also many standard card games: hearts, bridge, whist, poker etc. And appears to simulate a tabletop for playing with others or solo. I have not played it much but it seems intuitive as a platform for playing many different boardgames online, but is a bit clunky compared to a purpose-built online game. - Source: Hacker News / 5 months ago

Tabletopia. Web app, not many wargames available, I think. Game search is pretty rudimentary. Source: almost 1 year ago

Tabletopia - Free to start. Build games through their online editor. Source: about 1 year ago

Maybe look at finding online options for the "more strategic and lengthy board games"? I know there are lots of options for Diplomacy (which is especially suitable for online play, having discrete turns), but I'm sure you'll be able to find similar online portals for other games (e.g. https://tabletopia.com). Source: over 1 year ago

Boardgamearena.com and https://tabletopia.com/ have several more games for free as well. Table Top Simulator itself isn't free, but it does have a ton of free mods for board games. Source: over 1 year ago

Crosswords Arena is a pretty good multiplayer web-based Scrabble game. No download or signup required. Source: over 1 year ago