I just finished evaluating a bunch of feature flag platforms for my employer this past week. Self-hosting and having a .Net SDK was important to us. Below are the results.

Best options:

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    Flagsmith: has UI and can be self-hosted for free (BSD-3 license).

    GO Feature Flag: Completely free, but has no UI, although feature flags can be defined in JSON/YAML files checked into Github

    Flagd: Completely free, but has no UI.

    Statsig: Free plan covers our needs for a year or two. The .Net SDK is lacking, but we can use REST API instead.

Too expensive/cannot self-host:

    Growthbook

    Kameleoon

    Split.io

    DevCycle

    LaunchDarkly