If you have an Android phone: Flaming Durtles by @ejplugge [forum post]
If you have an Apple phone: Tsurukame by @davidsansome [forum post]
I’ve only had experience with Flaming Durtles as I have an Android phone, but I’ve heard good things about Tsurukame. Flaming Durtles has built in “scripts” such as lesson/review reordering/priority, lighting mode, etc, as well as offline reviews, so you can always stay on top of things. I believe Tsurukame has similar features.
If you want to check out more web scripts that may help (or not, certain scripts can certainly harm your learning experience if you abuse/misuse them), see this compilation post.