Just loading all feeds and keeping them in sync. I can use my phone, the website or my terminal client and at the end of the day I got my list of read and unread articles whether I'm on my phone or laptop
Not exactly a reader, but I use rss2email[0]. It’s pretty easy to setup, has optional HTML/CSS support, and I run a cron job to pull feeds daily. I like being able to browse through articles wherever I can get email without having to rely on a separate, proprietary service or self-hosting.
NetNewsWire for macOS/iOS[0]. It was the best RSS reader for Mac OS X in the far past and they have now revived it and made it open source. I particularly like that you can sync feeds via iCloud or self-hosted instead of an external service.
I use (and made) https://sumi.news - RSS, newsletter, and Twitter support. No subscription. Clean chronological feed, and a per-feed recent entry view.