The best alternatives to Sidebar are Suraj Keshri, Memex, and LaterBin. If these 3 options don't work for you, we've listed a few more alternatives below.
Axomark allows you to create bookmarks with password without signing up. You can then choose to share your bookmarks with or without edit rights. The shared bookmarks are synchronized and can only be accessed with a valid link.
With LeafPile you can collect and organize your inspiration, thoughts, images, videos, and links in once place. It is simple, easy to use and best of all free!
Unnon is a social app based on chats visible to anyone, even Direct Chats. You can create your own chat opened for anyone to join or password-protected; read, follow and join other chats. All with real-time translation. No use of personal data for tracking.