Postgresql looks awesome. It builds easily from source, and has a nice featureset given the cost. "Redgres" looked to be a pilot project, and given their link leading to a parked domain and the only link provided pointed an "alpha" release. Nobody is going to run production on an alpha version, so obviously we can't judge the popularity of T-SQL compatibility based on what looked to be a pilot experiment from a crew who probably couldn't follow through beyond an initial alpha release.