Believe me, I'm a great advocate of building the thing you need rather than blinding using libraries, but there's some great stuff out there: lessc, RabbitMQ (although that works well on Windows), Riak, Postgres, neo4j, hadoop, jQuery (Microsoft saw the light on that one), elastic search, pygments. Of those, Microsoft can offer alternatives to 2 of them: MSMQ and SQL Server. The others are sufficiently costly to re-implement that you're likely to just try to work around the problem (I'd love to see someone attempt a DB with Riak-like reliability on .NET... RavenDB is not that DB.)