Free Software Downloads

I’m trying to reconfigure my computer and I’m looking for a reliable, free website where I can download software for performance and maintenance. Also, my friend put this thing on my mom’s laptop, I can’t remember what it’s called, starts with an A and then two more capital letters haha, if that helps… but it’s a firewall, I think?! Anyways, if anyone could let me know what sites are the best to download free software and what that one program is called, please help! Thanks!!