LibreOffice is good as a standalone software, if you’re not looking for MS Office compability. I use LibreOffice, and my sister suddenly ask me to help edit their MS Office document. It was nightmare. There are a lot of hidden gotchas that rarely reported. It’s absolutely not recommended to constantly changing software if you’re editing your document.

Also, at the moment, Excel has more advance feature than LibreOffice Calc.

There is one: SuperTuxKart

It’s free and open source. There are plenty of community content, like custom karts and maps. It’s even adding game mode from popular game. The last one is from Rocket League.

Most of people are self-hosting the server. You can go to the official Discord or Any STK commmunity to find friends to play together :)