Garnet is a cache store from Microsoft Research that speaks the Redis wire protocol (RESP), so unmodified Redis clients in any language can connect to it. It supports much of the Redis API, including strings, sorted sets, bitmaps and HyperLogLog, and offers extensibility and transactional stored procedures. Garnet is written in C# on modern .NET, uses a storage layer called Tsavorite with tiered storage support, has a cluster mode with sharding and replication, and supports TLS. It runs on Windows and Linux and is installed by you, for example through Docker or NuGet.
Garnet is open source under the MIT licence and is developed by Microsoft, a US company. The sources describe no Microsoft-hosted Garnet service: you run the software yourself, so where the data resides depends on your own infrastructure, for example a European data centre or a European cloud provider. The project nonetheless remains steered by a US company, which is relevant to the continuity and direction of its development.