Zotero also usually imports article PDFs.
Reference Management Systems: Citations and Bibligraphies Made Easier
Reference management systems allow you to import, organize, and annotate citations from library catalogs and databases and the Internet. They also sync across multiple computers, allow the easy generation of bibliographies, and in some cases work within Microsoft Word and LibreOffice to add citations. If you see an article you like in a database, for example, click a button and it's added to the program. Organize citations into folders; click on a folder to generate a bibliography in the citation style of your choice.
Princeton University Library now supports an institutional subscription for unlimited storage (e.g., for article PDFs), authenticated with a current Princeton University email address. If you already have a Zotero account, but it’s not currently linked to your Princeton email, you can add your Princeton email in Zotero Preferences under Settings—> Account and the new unlimited storage will show up under Settings-->Storage.
PDF Storing, Managing, Reading, and Annotating
File Syncing and Storage Programs: Never Lose Your Work Again
File syncing programs allow you to save files to a drive on your computer that will be stored in the "cloud" and synced across multiple devices. They work like regular drives, so there's no uploading. You can sync a folder with multiple services. Working on that important project? Sync the folder with Dropbox, and then sync the dropbox folder with Sugarsync. That way your documents are on multiple computers and clouds.
Research Photo Management
From the creator of Zotero; helps organize and annotate research photos from archives, etc.
Organizing Notes and Other Information (personal knowledge base)
Handy for quick notes anywhere on your phone, but also potentially useful for saving, tagging, and organizing research notes and quotes as well as pretty much any kind of information. There are several of these. I use Bear Pro, simple and relatively inexpensive, but works only on Apple devices. Notion is more powerful, works well, and the "Personal Pro" option is free for educators, allowing you to synchronize across devices and operating systems, so register with your Princeton email. Obsidian is similar to Notion, and free to use on one device, with a lot of plugins to add other features, but pricey if you want synchronization. Evernote is free if you don't want to sync across multiple devices. OneNote comes with your university Microsoft account. Avidnote is a newer product "developed by a team of researchers and developers from Chalmers University of Technology located in Sweden."
There are several good options. I use Scanner Pro, available for Apple, which scans and OCRs text to create searchable PDFs. It's made by Readdle, which also makes my favorite PDF reader for Mac. CamScanner for Android also works well. Very handy for scanning a few pages of physical books and journals. Share PDFs or text with Google Drive, Dropbox, Evernote, email, etc.
Audio Recording and Editing
Foldable, Portable Book Stand
Again, many options. I have a couple of this inexpensive model. Holds books open and upright for reading, referring to when writing, or scanning with a smartphone scanner.
Line Break Removal Tool
Text copied from PDFs often has line or paragraph breaks you need to remove before pasting that text into something you're writing. Text Fixer strips out those line breaks.