I haven't contributed much to OpenSource, my goal is to contribute more in the future. However I have forked a GitHub repository and enhanced it.
PetaPoco is "A tiny ORM-ish thing for your POCO's", a "tiny .NET data access layer inspired by Rob Conery's Massive project but for use with non-dynamic POCO objects".
My commit includes a fix to support multiple primary key's in T4 generation as I couldn't find any other fork that supported this. My inserts/updates with multiple primary keys are now accurate as I believe they were innacurate before this modification. It also increased the speed of inserts/updates to table's with multiple primary keys. Has only been tested with MS SQL Server and requires .NET 4+.