Sirena is a pure Ruby implementation of Mermaid diagram rendering. It parses Mermaid syntax and generates SVG output using Parslet grammars and ELK layout. Supports 24 diagram types: flowcharts, sequence, class, state, ER, C4, block, architecture, Gantt, timeline, Git graph, mindmap, Kanban, user journey, pie, quadrant, radar, XY charts, requirement, Sankey, packet, treemap, info, and error displays.