What are the key differences between factom and tieron? At a headline level, both Factom and Tieron appear to offer an identical  service: ability to use the bitcoin blockchain to publish proofs of existence in a scalable way (i.e. by multiplexing multiple events into a single transaction, and therefore reducing the cost and overhead per event).

Are there any further fundamental differences:


in terms of service(s) offered to the end users?  
in terms of implementation specifics?
Factom seeks to be a distributed and autonomous protocol, like Bitcoin.  There is no terms of service. Instead, Factom uses a token (factoid) to reward servers for running the protocol.  Independently, the protocol requires users to use Entry Credits (which act like accounts) to create chains and add entries to those chains. Factoids are converted into Entry Credits.  

Since Entry Credits are not tradable, and only require requests be signed with the Entry Credit Key, users can buy Entry Credits from anyone who has factoids.  A user of the protocol never has to touch a tradable token.  Entry Credits are also managed at a constant dollar value; use of the Factom protocol carries no regulatory or currency risks.

Tieron does much of what Factom does as a centralized solution.  They provide digital receipts, but you do have to open an account and agree to their terms of service.  To use Tieron, you set up an account, and pay a subscription fee.  They have no token or altcoin.  This is simply a standard service company providing data integrity services for a fee.

Full discolsure:  I am the principle designer of Factom, which also benefited from design work and technical input from Wayne Vaughan, CEO of Tieron

Updated with a bit more information