Collabora Office. It's a free LibreOffice fork for iOS/iPadOs. I stumbled across it when I taught regular expressions to my pupils and only had MS Office at hand, on the school computers, which is crap at searching for pattern matches in documents. Libre Office is really good at that. And all my pupils have iPads and they could use Collabora Office.

I suppose I would choose Darcs & Pijul for version control systems to bit into Git hegemony (& if you prefer Git hegemony, don’t use proprietary code forges).

Additionally just the general vibes of IRC & XMPP for battle-tested chat applications that are lightweight for clients & servers alike. These are the kinds of tools your next community should be built on if you want to minimize resource usage (data plans, storage capacity, battery, CPU churn).