Open Data Portals

If you've ever clicked "download CSV" on a government data portal, you've almost certainly used CKAN. The category is unusually FOSS-dominant — the largest national portals run on open source. Pair with Civic Tech Overview, Budget Transparency, Investigative Tools, and Databases & ORMs for the data layer underneath.

Free / FOSS (start here)

• ★ ★ CKAN — AGPL-3.0; Python; the open-data portal. Powers data.gov (US), data.gov.uk (UK), open.canada.ca, the EU Open Data Portal, data.europa.eu, and dozens of national / municipal portals. Originally built by the Open Knowledge Foundation (2006); now stewarded by the CKAN Association. Mature plugin ecosystem (DataStore, DataPusher, Harvest). The default for any serious open-data portal in 2026.
• ★ DKAN — GPL-2.0; Drupal-based; lighter-weight than CKAN; used when an organization is already a Drupal shop. Built by Civic Actions.
• ★ Open Data Cat (OpenDataSoft Community Edition) — note: the OpenDataSoft platform itself is paid, but they publish open SDKs.
• JKAN — MIT; static-site generator approach to a data catalog (Jekyll + GitHub Pages). For small / lightweight catalogs without a backend.
• udata — AGPL-3.0; Python; powers data.gouv.fr (France); CKAN-alternative built by the French government's Etalab.

Paid SaaS (the proprietary half)

• Socrata (Tyler Technologies) — paid; the dominant US-municipal open-data SaaS; powers City of Chicago portal, NYC OpenData, SF OpenData. Acquired by Tyler in 2018; expensive; closed source. Many cities are migrating off Socrata to CKAN in the 2024–26 window when contracts expire.
• OpenDataSoft — paid; French SaaS; pretty UI; pivoting toward "data products" / API monetization.
• Junar — paid; Latin-American open-data SaaS; smaller footprint.
• OpenGov — paid; municipal-finance-leaning suite; some open-data features bundled.

Standards

• ★ DCAT — W3C standard; "Data Catalog Vocabulary"; how catalogs describe their datasets in RDF. CKAN exports DCAT-AP (the EU profile) natively.
• ★ DCAT-US 1.1 — US federal profile of DCAT; what data.gov ingests.
• CSV on the Web (CSVW) — W3C standard for adding metadata to CSVs; less adopted but useful.
• Frictionless Data — Open Knowledge Foundation; "Data Package" spec for bundling CSVs with metadata; widely used in research / civic data.

Harvesting / federation

• ★ CKAN Harvester — built-in plugin; pulls metadata from other CKAN instances, DCAT feeds, GeoNetwork, Z39.50, and arbitrary RSS/XML. This is how data.gov stays in sync with state-level portals.
• GeoNetwork — GPL-2.0; Java; geospatial-metadata-catalog cousin to CKAN; INSPIRE-compliant; common in EU geospatial data.

Honest take (2026)

• CKAN's dominance keeps growing — the cost of running Socrata renewals is forcing US cities back toward FOSS.
• The killer feature is the API. A CKAN-hosted dataset gets a JSON API, a CSV download, a SQL endpoint (via DataStore), and DCAT metadata for free. Researchers and journalists pivot directly to the API; municipal IT shops should treat CKAN as data-API-as-a-service.
• GIS-data interop is still painful. GeoNetwork + CKAN + ArcGIS Open Data Hub is the typical reality; none of the three integrate cleanly.
• The Frictionless Data spec deserves more adoption — CSVs with proper schemas (column types, primary keys, foreign keys, units) are dramatically more useful than naked CSVs.

What to actually do with an open-data portal

• Publish the canonical CSV + a stable URL. Bake the URL into the agency's documentation. Don't break it.
• Set a schedule. Monthly / quarterly / annual updates beat sporadic dumps.
• Tag with DCAT. Theme, geography, license, contact point.
• License clearly. US federal data is public-domain; most local-gov data is CC0 or CC-BY 4.0. See OSS License Selection for the CC-family.
• Don't build a bespoke portal. Use CKAN. The custom-built municipal data portal is the most consistent waste of civic IT money in the 2010–2025 era.

Pick this if…

• National / large-municipal portal: CKAN.
• You're a Drupal shop already: DKAN.
• Tiny catalog, GitHub-hosted: JKAN.
• France / French-language deployment: udata.
• You're trapped on Socrata and your contract is up: migrate to CKAN; Civic Actions / Datopian / DataLanding can help.
• Geospatial-metadata-catalog (INSPIRE / SDI): GeoNetwork.