The game was developed alongside Valve's Steam software and the Source engine.

Entity and relation annotations:
id: 0
type: entity
value: text: Valve
labels: <Organization>
id: 1
type: entity
value: text: Steam
labels: <Production>
id: 2
type: entity
value: text: the Source
labels: <Production>
type: relation
to_id: 1
labels: Organization:develops/produces/sells:Production
from_id: 0
type: relation
to_id: 2
labels: Organization:develops/produces/sells:Production
from_id: 0