I watched older video by Alan Kay and now I want to give a Squeak another try

It's definitely worth a closer look at! You might also consider Pharo and Cuis, both of which branched off Squeak developement after 1998 in order to pursue different directions. Pharo went for a larger system supporting small-scale commercial software development, whereas Cuis went for minimalism.

Cuis also some interested mathematical stuff! 🙂

with Cuis’ main developer Juan Vuletich by Kris Jenkins. This is the year of the Cuis!