Decide what you are actually replacing before you shortlist anything: an editor, a publishing workflow, a plugin platform, or a whole application runtime. WordPress lets themes, plugins, and content structure grow together, which is convenient until you need cleaner boundaries. A brochure site, a newsroom, a documentation hub, and a membership portal have very different needs for revisions, taxonomies, routing, and permissions, so match an alternative's content model to yours first. If your WordPress is really a blog with a newsletter bolted on, Ghost covers that natively; if it is a large content operation with many editors and content types, Drupal or Wagtail is closer to the shape you already run.
Expect the biggest gaps around the WordPress ecosystem rather than basic publishing. The familiar admin, block editing, one-click plugin installs, and off-the-shelf themes are hard to reproduce exactly, and most alternatives trade that convenience for something else: stricter content schemas, file-based workflows, faster rendering, or simpler operations. That can be a genuine win, but it moves work around. Editors may face more structured fields, designers rebuild components, and developers own deployment instead of installing another plugin. Grav and Bludit go furthest here, dropping the database entirely in exchange for a smaller, file-based site you version like code.
Migration usually starts with the built-in WordPress export, the REST API, or a database and uploads backup, depending on how customized the site is. Posts, pages, authors, categories, tags, comments, and media often extract cleanly, but shortcodes, custom fields, page-builder layouts, menus, widgets, and redirects need mapping or cleanup. Plan a content freeze, import into a staging site, crawl the old and new URLs, then ship 301 redirects before you move any traffic.
