Because Obsidian stores notes as plain Markdown in a normal folder, the switch is unusually painless - there is no proprietary database to escape. That means you are not really migrating data; you are choosing a different app to point at the same files. So judge these alternatives on workflow and licensing rather than on whether they can read your notes, because they almost all can.
The two things that differ most are sync and extensibility. Obsidian's own sync is a paid add-on, while several open alternatives offer a server you host yourself for device sync and end-to-end encryption, and any of them can sync as plain files through a tool you already use. Obsidian's large community-plugin ecosystem is also part of what people rely on, so check whether the features you depend on - specific plugins, canvas-style boards, particular link syntaxes - have equivalents in the app you are considering.
To move, copy your vault folder and open it in the new app. Standard Markdown, wiki-style links, and attachments generally carry over directly. The things to watch are plugin-specific syntax and any features that were really plugins rather than core Markdown, since those may render as plain text until you find an equivalent. Keep a backup of the original vault until you have confirmed everything you care about survived.