libbitcoin’s bitcoin-server on a VPS with 1 GB of RAM and 512 MB of swap, which is clearly not enough. The server starts getting killed for reaching an out-of-memory condition every minute or so after block #200000, even on Testnet.
It’s dirty and it clogs up fast, but it works.
Every OOM kill adds to the possibility of database corruption. So I sometimes back it up, too.