Your campaign is an important creation in your life that can bring you thousands of hours of joy. Don't lock it up with proprietary software, and don't rely on other people to preserve your campaign data.
Don't lock yourself down by writing your important campaign content in a virtual tabletop or cloud-based campaign tool. Use VTTs only for mapping and dice rolling. Character sheets, logs, and campaign writings should be kept in an open format that will survive the passage of time.
The best format for most campaign data is plain text. Markdown is a great format that can be read and edited by literally thousands of apps, including on your phone.
If you like to use a word processor, I recommend LibreOffice instead of Microsoft Word or Apple Pages, because it produces documents in an open standard format which will always be usable, no matter what Microsoft or Apple decide to do. The documents LibreOffice produces are also readable by Word and Pages, so they are very portable. If you have a friend edit your LibreOffice file in Word or Pages, make sure they save it in “open document format” before sending it back to you.
LibreOffice is also great for spreadsheets, which are fantastic tools for any campaign. You can do a lot of powerful stuff with a spreadsheet without needing to write your own software.
Other tools like LogSeq can be great too, depending on how you like to work on your campaign.
Always back up your data – campaign records, setting info, character sheets – it should all be backed up at least 3 different places. One of the backups should be stored in a physical location separate from the other two so your campaign will survive a fire or natural disaster. Try to make a backup at least once every week you play. Put a reminder in your task manager or to-do app, or set a weekly reminder in your phone.
Dropbox, Google Drive, OneDrive, and the like are not backups, they are sync. If your file gets deleted on your computer or phone, it gets deleted everywhere. Syncing services never count as backups.
If you find Demon Idol valuable and want to ensure you can use it for a long time, don't rely on us to host it! What we mean is: a website could go down at any time. You should keep copies of gaming tools that are important to you! You can email firstname.lastname@example.org and we will send you an archive of every page on this website, any time. Eventually we will set up a way to download it yourself, and perhaps obtain it in a printable book-like form.
Note that you can also download any page in PDF format using one of the buttons on the right hand side of the screen. The PDFs even include a QR code you can scan on your phone to open the page on your device.
By the way – this goes for every service you use. Would your campaign be fine if a service you use shut down tomorrow, lost your data, or had a security breach?