The best alternatives to Sidedrive are Meta Search, Needl, and Interappy. If these 3 options don't work for you, we've listed a few more alternatives below.
Needl lets you instantly find any document, message, or file you need. We're a single, intelligent search bar for all your web apps. Get started today for free at https://www.needl.tech/
Interappy helps you get a handle on your Google Drive! Turn the associations and links you naturally create in your sheets, docs, and slides, into easy to navigate link cards. You'll feel like you have gained superpowers, finding the docs you need in seconds!
Milo is the smart, secure way for you to search across google drive without tab surfing. Milo pulls up the exact page containing the information you need. No one gets access to your docs unless you share them, and all your data is stored in your device cache.