Line of sight calculator: In Northern Colorado, many repeaters take advantage of the mountains to gain height. However, when you are close to the foothills like I am, you can be in a shadow. Meaning there are mountains between you and the repeater. The map below shows my location and a random point in the mountains west of me.
GridTracker2: This is one of the coolest things to hit ham radio since FT-8. If you do FT-8. This is a must-have add-on
ADS-B Exchange-Flight Tracker. Fellow aviation nuts will love this one. See what’s flying overhead in real time.
Colorado Digital. A group of digital amateur radio enthusiasts who experiment with, build, and maintain a system of multiprotocol talkgroups. We bridge together D-STAR, DMR, YSF (C4FM), WIRES-X, NXDN, P25, and other stuff under different talkgroups, helping to make it possible for amateurs to talk to each other no matter what digital mode they are using. We are not a traditional club, though we do have a club callsign (W0CDM).
Below are just quick add-ons. I will add descriptions later
https://www.pulsepoint.org/https://www.pulsepoint.org
https://www.wsprnet.org/drupal/wsprnet/map
https://www.liveatc.net/search/?icao=kfnl