The following is a semi-comprehensive and heavily opinionated list of types of generic applications you'd expect to see preinstalled on a modern consumer device. There's no exact reason why I created this other than the fact that I couldn't find anything like this online. I guess you can use this if you're making a toy OS and you're lacking ideas.
Productivity
- Calculator
- Calendar/daily planner
- Clock/timer/alarm
- Contact browser
- Dictionary browser
- Map/navigation utility
- Notes editor
- Presentation utility
- Spreadsheet utility
- Todo/checklist editor
- Translation utility
- Weather forecast utility
- Word processor
Data manipulation
- Audio editor
- Audio player
- Bitmap image editor
- Font editor
- Font viewer
- Hex editor
- Image viewer
- PDF/E-book viewer
- Text editor
- Unicode character browser
- Vector image editor
- Video editor
- Video player
Networking
- BitTorrent client
- Email client
- Fax utility
- Password manager
- Phone dialer
- SMS messenger
- Two factor authentication utility
- Web browser
Peripheral hardware access
- Audio recorder
- Camera capture utility
- Paper scanner utility
- Printer utility
- QR code/barcode scanner
- Step counter/fitness assistant
System maintenance
- Antivirus utility
- Application log viewer
- Backup utility
- Bulk rename utility
- Checksum utility
- Data recovery utility
- Disk cleanup utility
- Disk image browser
- Disk image writer
- Disk partitioning utility
- Disk usage analyzer
- File archiver
- File browser
- File transfer utility
- File/disk encryption utility
- Hardware information utility
- Hardware resource monitor
- Help browser
- Network analyzer
- Process browser
- Process scheduler
- Remote desktop client
- Screen capture utility
- Software repository browser
- System configuration utility
- Terminal emulator
- Virtualization/emulation utility