While Zoho Docs offers native applications for desktop and mobile, you can choose to use the webapp which doesn't require you to download anything and can be accessed from anywhere where there's an Internet connection and a modern web browser.
Zoho Docs has 2 paid plans - $5/user/month and $8/user/month that add additional functionality and increase the storage limit. Compared to standalone purchases, the subscription fees can quickly rack up, especially since they are on a per user basis.