An internal combustion engine system comprising - an internal combustion engine provided with at least one cylinder, - an air intake system arranged to feed air to the at least one cylinder, - an exhaust gas system arranged to feed exhaust gas away from the at least one cylinder, - a turbocharger arrangement comprising a turbocharger turbine operatively connected to a turbocharger compressor, wherein the air intake system is arranged to feed intake air via the turbocharger compressor and wherein the exhaust gas system is arranged to feed exhaust gas via the turbocharger turbine so as to drive the turbocharger compressor, wherein the internal combustion engine system further comprises a turbomachine arranged in the exhaust gas system downstream of the turbocharger turbine, characterized in that the turbomachine is a positive displacement machine configured to displace gas from an inlet to an outlet thereof by trapping a fixed amount of gas and forcing that trapped amount of gas from the inlet to the outlet, wherein the internal combustion engine system further comprises a variable drive unit arranged to drive the positive displacement machine, and wherein the internal combustion engine system is configured to control the drive unit so as to control a flow of exhaust gas through the positive displacement machine, wherein the internal combustion engine system is configured to control the drive unit so as to operate the positive displacement machine in at least a first mode where a pressure ratio given by a pressure at the outlet of the positive displacement machine divided by a pressure at the inlet of the positive displacement machine is above 1, wherein the internal combustion engine system is configured to control the drive unit so as to operate the positive displacement machine in at least a second mode where a pressure ratio given by a pressure at the outlet of the positive displacement machine divided by a pressure at the inlet of the positive displacement machine is below 1, wherein the internal combustion engine system is configured to control the drive unit so as to operate the positive displacement machine in at least a third mode where a pressure ratio given by a pressure at the outlet of the positive displacement machine divided by a pressure at the inlet of the positive displacement machine is substantially equal to 1, and wherein the internal combustion engine system is configured to operate the positive displacement machine in different modes or drive levels in dependence of an operating mode of the internal combustion engine. - an internal combustion engine provided with at least one cylinder, - an air intake system arranged to feed air to the at least one cylinder, - an exhaust gas system arranged to feed exhaust gas away from the at least one cylinder, - a turbocharger arrangement comprising a turbocharger turbine operatively connected to a turbocharger compressor, wherein the air intake system is arranged to feed intake air via the turbocharger compressor and wherein the exhaust gas system is arranged to feed exhaust gas via the turbocharger turbine so as to drive the turbocharger compressor, wherein the internal combustion engine system further comprises a turbomachine arranged in the exhaust gas system downstream of the turbocharger turbine, characterized in that the turbomachine is a positive displacement machine configured to displace gas from an inlet to an outlet thereof by trapping a fixed amount of gas and forcing that trapped amount of gas from the inlet to the outlet, wherein the internal combustion engine system further comprises a variable drive unit arranged to drive the positive displacement machine, and wherein the internal combustion engine system is configured to control the drive unit so as to control a flow of exhaust gas through the positive displacement machine, wherein the internal combustion engine system is configured to control the drive unit so as to operate the positive displacement machine in at least a first mode where a pressure ratio given by a pressure at the outlet of the positive displacement machine divided by a pressure at the inlet of the positive displacement machine is above 1, wherein the internal combustion engine system is configured to control the drive unit so as to operate the positive displacement machine in at least a second mode where a pressure ratio given by a pressure at the outlet of the positive displacement machine divided by a pressure at the inlet of the positive displacement machine is below 1, wherein the internal combustion engine system is configured to control the drive unit so as to operate the positive displacement machine in at least a third mode where a pressure ratio given by a pressure at the outlet of the positive displacement machine divided by a pressure at the inlet of the positive displacement machine is substantially equal to 1, and wherein the internal combustion engine system is configured to operate the positive displacement machine in different modes or drive levels in dependence of an operating mode of the internal combustion engine.