In our Zoho suite, popular services such as Zoho Writer and Zoho Show already run on a grid of servers. This means huge improvements in reliability, with downtime becoming negligible. They can also handle more concurrent users, as we keep adding more servers to the grid. In grid based systems, individual servers can come and go without causing service disruption. Zoho Sheet and Zoho Creator are still transitioning to the grid, and this process is expected to be complete within the next month. Zoho Creator is particularly challenging because database schemas for user applications can evolve. Our grid software makes some assumptions about schema evolution, which most other applications satisfy, but not Zoho Creator. This means some additional custom work, hence the delay.
Until that is complete, we are stuck with care-and-feeding the servers periodically. Data is backed up both in real time on disk and off-line so this is not a data protection issue, but more of a service availability issue.
Please accept our apologies for this service downtime. Once we move to the grid, this issue will not recur.
Update: It is up now.