I don't understand. Is there already a foss version or is it just their goal?

"Versions
Molly, like Signal, uses Google’s proprietary code to support some features.

Molly-FOSS is the community effort to make it 100% free and open-source." 

 two versions. i recommend molly-foss 

 cool stufd. you can read up on the differences here: https://github.com/mollyim/mollyim-android