In order for Cardano users to hold their Ada securely offline, we are building support for the Ledger cryptocurrency hardware wallet. The first stage of this is to build the Cardano application that runs on the Ledger device itself, and this stage has been completed.
The project is progressing to add further integration with both Yoroi and Daedalus.
Currently, the project is waiting on the upcoming Ledger 1.5 firmware release. This is one of the dependencies currently holding back the completion of the integration. Unfortunately, Ledger have not been able to give precise estimates for a 1.5 release date yet, but we will provide updates when they become available.
Charles Hoskinson also provided a brief update on Ledger integration in his December video, which you can watch and read about here.
And you can always check the Cardano Roadmap or the Weekly Technical Reports for updates!
Emurgo has been working with Trezor to integrate Yoroi, their light-client Chrome extension wallet. They will be releasing an update on this project next week!