Modern aircraft have a number of systems to their disposal to enhance flight safety. The common term you will hear is aircraft collision avoidance systems. These systems range from radar, TCAS, portable CAS, terrain awareness system (TAWS), ground proximity warning system (GPWS), synthetic vision in EFIS and the obstacle collision avoidance system.
For the experimental homebuilt aircraft pilot these are usually quite expensive systems, except for the portable CAS and the good old see and be seen system (which has its flaws). New ADS-B In solutions nowadays offers a receiver with connection to a mobile device as weather/ traffic display.
For the aircraft homebuilder it might be interesting to try to build and ADS-B receiver yourself. Or shop for the most affordable solution available, this article might be of some help to you!
There are several portable/ mobile systems in use today: Stratux, FLARM, Merlin and PilotAware (the last two use a Raspberry PI and a GPS, RTL and Wifi dongles) to name but a few. These require your to assemble all parts and together with two antennas and an USB power bank you will be ready to go for the least amount of money spent. Although some can be bought pre-built, either through Amazon or pilot shop.
Garmin offers a portable solution (GDL 50 series) which also includes subscription free weather including NEXRAD radar, METARs, TAFs, TFRs, AIRMETs, SIGMETs and NOTAMs. The GDL 52 combines ADS-B weather with XM for your portable device via Wifi.
This company (www.appareo.com/aviation) sells the Stratus series of ADS-B solutions. The latest version is the Stratus 3 with WAAS GPS, AHRS, Flight Data Recorder, pressure sensor and Wifi. Appareo offers all three ADS-B options for a reasonable price. Can be used with multiple EFB apps.
Uavionix (www.uavionix.com) sells a number of ADS-B in and out (transponder) solutions for the experimental and light sport market, the Scout and Sentry (for use with ForeFlight only) being the latest and greatest. They even carry mini ADS-B units for drones!
ForeFlight (https://foreflight.com/connect/) in cooperation with Uavionix also sells three portable ADS-B solutions:
The first one is called the Sentry with full capabilities but its only for the ForeFlight app. It has an AHRS backup with CO monitor, barometric pressure sensor and an internal 12+ hour battery.
The Sentry is also available in a mini, card deck sized version without AHRS, barometric sensor or CO detector and uses an external power source.
The ForeFlight Scout (somewhat similar to the Sentry mini but a different form factor) is the cheapest ADS-B solution but it does not have built-in battery, a backup AHRS or CO detector.
Levil Aviation (levilaviation.com) sells a combined wing light beacon system. The unit looks like a mini fin which has a pressure sensor, transponder receiver, GPS receiver and an ADS-B Out system. It mounts on the belly of the aircraft and needs a separate GPS antenna, listens to your transponder code and sends out the ADS-B data. They even have an under the wing mounted unit, BOM.
Dynon Avionics (www.dynonavionics.com) sells a portable ADS-B solution in the form of a small device capable running a weekend long and its called the DRX. It sits between the full blown and the 'do it yourself Raspberry PI' solutions. The DRX has a dual band ADS-B receiver and supports the GDL-90 protocol via Wifi to numerous compatible applications as ForeFlight, FlyQ, SkyDemon (SD needs a barometric indication which the DRX does not have) and more.