SpringNotes is described as 'Write styled Markdown notes, sync across Mac, iPhone and iPad add to-dos and tags, export to a variety of formats and choose your favourite style from a variety of colourful themes' and is a Note-taking Tool in the Office & Productivity category. There are more than 100 alternatives to SpringNotes for a variety of platforms, including Windows, Mac, Linux, Online / Web-based and iPhone. The best alternative is Joplin. It's not free, so if you're looking for a free alternative, you could try Standard Notes or Microsoft OneNote. Other great apps like SpringNotes are Obsidian (Free Personal), Google Keep (Free), Evernote (Freemium) and Typora (Paid).
Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, can be copied, tagged and modified either from the applications directly or from your own text editor.
Zettlr is a supercharged markdown editor that combines many writing editor features and collect them in one application. It aims at speeding up your workflow and help you write without any interruptions.