I’m keeping it simple today with a few recommendations for RPGs which work well for open table play. Because I often have people new to my table, and sometimes new to Roleplaying, joining in I like to keep things simple. This also helps us spend more time in the roleplaying rather than in character generation or prolonged combats.
OSR RPGs work well because most people expect D&D and have watched some actual plays or played some Diablo. Also the conceit of Adventurers in a fantasy world makes it really easy to bring in new PCs each week and there is no shortage of small dungeons to run them through. Iron Falcon worked really well, it’s a very tidy rewrite of D&D as it was in 1975. It’s free in PDF and available POD from Amazon for a very reasonable price.
Similar but even lighter is The Vanilla Game. It’s a complete OSR RPG available online. You can easily run it off your mobile and your players can all look up their own spells and equipment as they need them. TVG features some wonderful quality of life improvements on the OSR formula including simpler classes, equipment slots which you can define as you need them, and an intuitive task resolution system which, erm, I wrote.
Offworlders Is a wonderful space adventure game. Characters are Scoundrels, Techs, Psychics and Soldiers each with a few abilities to pick from. The group gets some blasters and a ship and you are good to go. The rules are pared-back Powered by the Apocalypse and I find it pretty effortless to run. This one is also free at drivethrurpg.
Harder to explain is Troika! Imagine the official RPG of the best cartoon never made. Troika is a city somewhere in the middle of the hump-backed sky, connected to countless worlds by portals and golden barges. Players are given total weirdos to play and in my experience everyone loves it. The complete rulebook is available free on the website.
If you are running something modern day, you can’t really go wrong with Liminal Horror. It has only the essentials, that is saves to avoid harm which are also stats to track harm, also equipment and a system for panicking. I love it and character generation takes less than five minutes. Again, Liminal Horror is free and available in full in a webpage.
Ominosity 
I’d heard of Liminal Horror, but never actually looked at it. It’s quite cool to discover that it’s an Into the Odd derivative!