Basics

Essentially Chafing Fuel but without the can
So either in bulk, or in a small plastic bottle (akin to Lighter Fluid or tube (akin to toothpaste))
Main advantage is reduced spill risk and POTENTIALLY less risk of Boiling Fluid in more improvised/simple Spirit Burner setups
Downsides are cost, residue after burning (depending on what gelling agent/dyes and other additives are, and more difficult dispensing (Gel/Paste vs a Gas/Liquid etc)
Also can be used as a firestarter/“liquid tinder”, as a safer alternative to Liquid Lighter Fluid (or Gasoline/Diesel Blends, using just the former is notoriously hazardous due to the vapor cloud)

Brands

Probably similar to what they sell in the capsules designed to replace Hexamine Fuel Tablets , although potentially more “liquidy”?
Clear with little resedue
An Amazon Listing for “Fire Dragon Gel Fuel” ( ‘’’~22 USD as of this edit’’’ )
- Although with it being a UK based company, may be some tariff shenanigans there, either way too pricey to make sense here in the USA really
- 250ml bottle

Blue, uncertain on residue upon burning
An Amazon Listing for “Rutland One Match Gel Fire Starter” ( ‘’’~21 USD as of this edit’’’ )
946ml (32floz) Bottle

Green, decent amount of residue leftover when used on it’s own
- User: Eric here, it basically looks identical to the stuff in the bioethanol sterno cans
An Amazon Listing for “ Sterno Fire Starter, Ethanol - Firestarter Instant Flame Gel” ( ‘’’~22 USD for a 3 Pack of Bottles as of this edit’’’ )
- Sold in 454g (1lb) Bottles
- Odd that weight is used rather than volume

Trangia Offers a Gel Burner that is compatible with their Windshield system
It’s basically just a round Metal “tin” with a snap on lid and an embossed logo in the bottom
It does nest/stack well though, so especially given it can even run on Gel Hand Sanitizer etc, it’s a neat capability to have
Their Page on the Product
An Amazon Listing for “ Trangia - Aluminum Gel Burner | Use with Gel and Solid Fuel”
- As they state it also can work with Hexamine Fuel Tablets / other Smokeless Fuel Tablets such as the BCB Fire Dragon Solid Fuel Tablets etc