Below is a list of applications for training at home, on your schedule, several of the major aviation companies’ navigation, EFIS (Electronic Flight Information System), and often combined communication systems.
The venerable Garmin G1000 PFD and MFD simulator from Simionic ($10 each) is considered the best simulator you can get for this avionics suite. The ultimate setup is to use two modern iPads with one running the PFD and the second running the MFD app (they talk to each other over WiFi). You can also tie them into X-Plane for the ultimate real-time simulator experience.
Garmin doesn’t provide a G1000 simulator any longer, but you can buy their G1000 software from MyPilotStore. For most GA pilots the Cessna NAV III choice will probably be the most appropriate.
Garmin does have the G1000 NXi simulator available for $50.
For the older, but still widely used Garmin 400W and 500W-series nav/comm systems you can download free applications for installation on your PC here.
For learning the Garmin GTN, G500/G600 TXi, GDU 620, GNX 375, GNC 355/355A, and GPS 175 units there is a free PC download available here.
Garmin does have an iOS app for their TXi system available here.
Garmin does have an “app” for their GTN650/750 system available in the Apple store, but it is basically a series of videos in the app and not a simulator which includes a $40 in-app purchase for more content, so we won’t bother linking that here.
Avidyne’s iOS tablet app for their IFD series systems can be found here.
Dynon doesn’t have a trainer app or software for their SkyView product (very disappointing), but they do have a few training videos on YouTube to help a pilot learn something about them.
Many older airplanes have replaced their vacuum systems with one or more uAvionix AV-30 attitude/heading indicators. You can download a simulator to become familiar with the button functions and menus from their site here.