Ethereum: no, it doesn't use ethereum, it could support advanced smart contracts if you're willing to fork counterparty/rootstock/omni for the gridcoin network. You can trade ETH:GRC on the BTS DEX.

Golem: Their project isn't in production, they performed an ICO (GRC performed a fair distribution based on BOINC contributions), Gridcoin provides computation for free where as Golem charges money, GRC > Golem.

Steemit: The Gridcoin community is using Steemit to promote itself, we've been using the platform for like 9-10months now.