Android Superlist A good looking to-do app with support for notes, inline images, and collaboration features with a generous free plan or $10/mo for Pro plan.
Markdown SilverBullet An open-source, fast, WYSIWYG, and free Progressive Web App (PWA) that supports Markdown, templates, queries, and cross-device synchronization. Incredible!
Android RetroNote Free, and fast, supports Markdown, multi-level tags, Google fonts, linking of notes, and a graph view, and it's completely Web-based so there's no app to install
Android myReach Definitely worth checking out, a ton of functionality, great support, apps for different platforms, and a useful AI tool to summarize your notes or help you write, but no Markdown input.
Android Nuclino Nuclino is really fast, beautifully designed, supports Markdown for input and output, has amazing version history, tables, an API, and has oodles of integrations. Great for teams.
Markdown Coda Well designed from a UI perspective and has WYSIWYG editing using Markdown syntax but a significantly limited companion to their Web app.
Android Notedex Notedex uses a cue card metaphor for the interface. You can put text, images, and draw on cards, flip them around and put content on the back. It's fun to play with but needs a facelift.
Android Nimbus Supports Markdown, linking of notes, versioning of notes, great table of contents, lots of online help, inline drawings and images, sharing a public link to a note, notifications, and filtering.
Web Chamu A Web-based note-taking app supporting Markdown, image attachments, easy table creation, and it has an open-source API.