OpenTimestamps is a timestamping service created by Peter Todd in 2016. He operates two servers providing the service and has written a Python tool and library for creating and verifying timestamps on arbitrary files.
Using these tools, users can create timestamps on arbitrary files, which will appear to them as small binary files ending in the extension .ots. These files describe how a given file is committed to by some Merkle root, which in turn is attested to have existed at some time.
Initially the attestation consists only of the URI of some timestamping server, which is accumulating commitments from many sources into a single Merkle root. Eventually the server will publish a Bitcoin transaction which commits to this root, producing a Merkle path from every committed document to some Bitcoin block's header. Users can obtain the full Merkle path by querying the server that produced the transaction. Anyone in possession of this path may verify the timestamp by querying the chain of Bitcoin block headers; the original server is no longer necessary.
This site provides a human-readable view of the contents of .ots files so that users can verify for themselves that their timestamps are legitimately committed to by the Bitcoin chain. It is for fun and education.
To view the contents of a Timestamp file, upload it here: