Feature parity across all platforms (desktop/web & mobile) is something that's being worked on, but for now, here's a list of differences between these two platforms:
Mobile-only
- Delete scheduled reminders
- Toggle whether metadata is shown (main view and master list)
- Toggle whether completed tasks are shown in projects
- List of Reminders (can be made on web/desktop)
Desktop/Web-only:
- Outlook calendar sync
- Calendar view
- Beat the clock
- Truncated list
- Task jar
- The wall
- Snooze (it's possible to have a list of Snoozed tasks)
- Change main view layout
- Project fullscreen
- Create/Edit recurring tasks
- Edit time track data
- Print lists
- Project shortcuts/Project focus picker
- Skinny sidebar
- Custom squares
- Custom text links
- Week Scheduler
- Planning Ahead
- Affirmations
- Procrastination wizard
- Dashboard
- Saved items
- Pinned tasks (it's possible to schedule & complete them)
- Top mini list