LimeSurvey

LimeSurvey is a mature, open‑source survey engine that delivers end‑to‑end data collection, analysis, and reporting. From a technical standpoint it exposes a rich REST/JSON‑RPC API and a legacy XML‑RPC interface, enabling developers to programmatically create surveys, push responses, or harvest statistics. The platform is built on a classic LAMP/LEMP stack with PHP 7.4+ as the application layer, and supports several relational databases (MySQL ≥ 8.0, PostgreSQL ≥ 12, MariaDB ≥ 10.3, or MSSQL ≥ 2016). Its modular architecture allows for granular permission control, multi‑tenant survey hosting, and extensive customization through themes and JavaScript hooks.

• Core Framework: PHP 7.4+ with Composer‑managed dependencies, following MVC conventions. The codebase is split into core, plugins, and themes directories, each with its own autoloading rules.
• Database Layer: Doctrine‑style PDO abstraction; schema migrations are managed by a custom migration tool that can be run via CLI or the web UI.
• Web Server: Apache 2.4+ or Nginx 1.x with PHP‑FPM; URL rewriting is required for clean routes (/admin, /survey, etc.).
• Caching: Opcache and optional Redis/Memcached for session and query caching.
• Front‑End: Vanilla JS with optional jQuery for legacy plugins; CSS is output via SCSS, allowing theme overrides.

• Survey Design API: Create/modify surveys, question groups, and questions through REST endpoints (/api/v1/surveys). Supports conditional logic, validation rules, and quota management.
• Response API: Submit responses programmatically (/api/v1/responses) or retrieve them for downstream analytics.
• Export Engines: Built‑in CSV, XLSX, STATA XML, and JSON exporters; developers can hook into the export pipeline to add custom formats.
• Authentication & Authorization: Pluggable auth backends (LDAP, CAS, SAML, OAuth2) and fine‑grained ACLs for survey owners vs. respondents.
• Webhooks: Trigger HTTP callbacks on events like survey_created, response_submitted. Useful for CI/CD pipelines or data pipelines.
• Audit Log: Plugin that records all admin actions, exportable via API for compliance.

LimeSurvey is fully self‑hosted and can run on any LAMP/LEMP stack. For production, the recommended setup includes:

• Containerization: Official Docker images are available on Docker Hub (limesurvey/limesurvey). Compose files expose volumes for data, plugins, and themes.
• Scaling: Horizontal scaling is achieved by sharing the same database instance; session data can be persisted in Redis to keep state across pods.
• Backup: Database dumps plus public directory snapshots; the API offers /admin/backup endpoints.
• High Availability: Use a load balancer in front of multiple web nodes; ensure that the database is configured for read‑replicas to handle heavy analytics queries.

• Plugin System: Developers can write PHP plugins that hook into lifecycle events (onSurveyCreate, onResponseSubmit). The plugin API is documented in the manual and includes event names, payloads, and return expectations.
• REST API: Fully documented with OpenAPI spec; supports OAuth2 for secure access. Rate limits can be configured in config.php.
• Webhooks & Callbacks: Custom URLs can receive JSON payloads; this is ideal for synchronizing LimeSurvey data with external CRMs or BI tools.
• Theme & Question Types: Themes can override CSS/JS and template files; new question types are added via plugins that implement the Question interface.
• Third‑Party Integrations: Built‑in connectors for Google Analytics, SAML, LDAP, and SURFconext; developers can extend these via the plugin API.

• Documentation: The official manual provides a comprehensive developer guide, API reference, and plugin development tutorials. Inline code comments are plentiful.
• Community: Active forums, a Discord channel, and an issue tracker on the bug‑reporting site foster rapid support. The community contributes plugins that cover most niche use cases.
• Testing: PHPUnit tests are included; CI pipelines run on GitHub Actions. Developers can fork the repo and run composer install to get a testable environment.
• Configuration: All runtime settings live in config.php, which can be templated for environment variables. This makes it straightforward to deploy across dev, staging, and prod.

1. Enterprise Feedback Loops: Companies can host internal surveys for employee satisfaction, automatically ingest responses into their HR analytics stack via webhooks.
2. Academic Research: Universities can deploy multilingual, quota‑controlled surveys and export data directly to SPSS or Stata for statistical analysis.
3. Event Management: Event organizers can generate post‑event feedback surveys, embed them on event pages, and use the REST API to pull results into dashboards.
4. Compliance Audits: Governments or NGOs can host GDPR‑compliant surveys, leveraging the audit log and data anonymization features to satisfy regulatory audits.

• **Open