How about you all?
High-throughput in-house network management (now libsnmp-based, formerly bespoke code). Lots of little glue services e.g. tail a log using "tail -f" and a process protocol, extract stats, answer SNMP queries for those stats via a unix socket passthrough from the net-snmp snmpd daemon. A couple of web servers; including one that parses a FreeRadius SQL accounting database and issues either a PB-based, SNMP-based or Radius packet-of-death based disconnect for kicking newly-banned users. A couple of misc daemons; e.g. one on our mail relays that will run an MD5 of a file in the filesystem on request from a Unix socket (in a pyrex GIL-release thread using the OpenSSL functions) so we can block all instances of a specific attachment by MD5 at SMTP-DATA-time. A very clever app that a colleague wrote that uses the QUEUE target of iptables to get TCP port 443 SYN packets from a walled garden network; then connects to that SSL service and gets the certificate; then permits or allows the original SYN based on a name-based wildcard of the certificate CN. Loads of other misc stuff mostly in this vein. It's a great.