These thumb shifters from microSHIFT are light weight, CNC machined and can be switched to friction shifting. This makes them preferred for touring/randonneuring bikes because they ensure that you can continue your ride even if indexed shifting runs into issues.
This particular model works with Shimano 10 speed MTB drivetrains. It can work with double or triple cranksets. By default the rear shifter is indexed but has an option to switch to friction. Front shifter is friction only.