My suggestions, in no particular order, are:
FAST AND DIRTY, Generic Wargame Rules for Fast & Dirty Modern and Sci-Fi Combat. These were originally developed by Ivan Sorensen (aka Nordic Weasel), who posted them to the web as free to use (generous soul that he is). However development has now been taken over by an alien collective. Sorry, I mean a community of sci-fi wargamers, who are still publishing the rules to the web for free download. The community seems very active. Go here https://www.fadwargame.com/ to find these. You can still download the originals via the FreeWargamesRules website, here https://freewargamesrules.fandom.com/wiki/F.A.D., if you prefer. If I recall, the rules lean more towards platoon than company level games.
FUBAR, originally by Craig Cartmell (author of In Her Majesty’s Name steampunk rules) gives a very good game at platoon level but might struggle with anything much bigger. Very much worth a look though, especially as it’s free, it comes on one or two sides of A4 and the community of users have developed a number of variants, mainy of which are sci-fi focussed. You can find FUBAR and variants here https://fubarwargames.wordpress.com/downloads/. If you decide to give them a spin then no matter which variant you try out for sci-fi, read ‘FUBAR – The Lanse Tryon Files’ at https://fubarwargames.files.wordpress.com/2014/07/ldt-fubar_v2015-04-17_01.docx . This is a mod by Lanse Tryon that fixes what some people see as a major wrinkle in the standard FUBAR ruleset, which is that ‘average’ units seem hard to activate. That spoils the game for some people (but not everyone). Lanse has also clarified a few other aspects of the rules that were occasionally the source of some confusion.
If your leaning is towards a decent (some say) 40k clone then take a look at ‘In The Emperor’s Name’, available free at try https://iten-game.org/ . ITEN is a fork from the FUBAR stable but not a clone of FUBAR. I have no interest in 40k clones so I haven’t looked at it and therefore have no opinion to share.
Other good options, paid for but not expensive.
From Nordic Weasel and available on Wargames Vault for $5 to $15:
LaserStorm is 6mm science fiction on a massive scale. Each troop stand is one vehicle or a 4-6 person fireteam. Units are platoons and the game can scale up to an entire battalion on the board, if you have the table space.
Company Commander in spaaace. This supplement extends Ivan’s Five Core Company Commander, which deals with modern (20th – 21st C) company level combat, into sci-fi conflicts. You’ll need the base game to play the extension, I think. I haven’t played the sci-fi game but I’m a huge fan of the standard game. That said, Ivan’s rules are innovative, so perhaps an aquired taste. On the other hand, they’re not expensive. Buying the core set and the supplement will only set you back $11.
Squad Hammer Core may also be worth a look but read up on it first. It definitely is innovative and a bit of a sandbox system but it is on pay what you want at the moment.
From Two Hour Wargames take a look at the 5150 series of games, specifically 5150 Platoon Leader (currently $10) or 5150 Battalion Commander (currently on offer at $5). The core of these rules is formed around THW’s ‘Chain Reaction’ system, which is available free to download and try from the Two Hour Wargames website. Even more than Ivan’s rules, Chain Reaction is like Marmite, you probably either love it or loathe it. I think the system is brilliant and an absolute delight to play but then I like marmite too. There’s review of 5150 Platoon Leader here https://geekken.wordpress.com/2014/03/26/review-5150-star-army/, if you’re interested.
Hope all that helps. Good hunting and best regards, Chris
PS I like your blog, keep it up. 😉