Disclosure I'm the CEO of Eris Industries
eris is a blockchain application platform which normalizes many development activities when building a blockchain backed application. It is agnostic as to what the underlying blockchain technology; although admittedly when using some blockchain clients eris provides nominal value beyond configuring, starting and stopping (e.g., it doesn't currently allow you to, say, put an EVM over Zcash).
With respect to smart contract enabled chain clients eris provides a range of tooling beyond simply configuring, starting and stopping chain clients.
We do make a blockchain client as well, called eris:db. eris:db was the first to market with a permissionable blockchain design. It is a tendermint consensus engine connected to an application manager (which contains a permission layer) connected to a built to specification EVM. eris exposes a lot more tooling around eris:db (via the eris chains namespace) as permissionable chain clients have more complexity to properly work with.
We think that right now the EVM is the market leading smart contract interpreter and it is true that we have a range of tooling around the EVM.
I've answered more of the differences between geth and eris:db here.