Sorry if posted somewhere else suburban Glasgow have released a new Scottish route for TSC “the buchan line” https://store.steampowered.com/app/3403000/Train_Simulator_Buchan_Line_Aberdeen__Peterhead/
I've had a go at one scenario this morning. It's pretty nice, from what I've seen so far. Very redolent the Weardale network and the same era. Lots to see and some tricky grades to get around, otherwise watch those career points disappear.
I'm not sure about the relationship. Suburban Glasgow grew out of the freeware route of the same name (which is still pretty good), being released commercially after having some 'professional' work done on it. He used to post a lot on the old UKTS forums. He's also done the merge between the various routes that make up the full-length West Highland Line on his own website, and some scenario packs available through Steam. I didn't think that they were related, although someone has attributed the Airdrie Extension to Rivet, even though it has a Suburban Glasgow credit.
Steam now lists a load of former Rivet DLC as Suburban Glasgow Ltd. I don't know what's going on, but there must be some tie-up. I see that on Rivet Games website they are now only showcasing TSW products. I suspect the TSC 'legacy' catalogue may have been passed over to Suburban Glasgow, though whether they are a Rivet brand or completely separate I can't say.
I've had a run down the route in a Stanier Mogul, the scenery is nicely done and has quite a unique feel to it. Aberdeen is also suitably grey and depressing, set the season to autumn and the weather to rain and you can capture the true misery of acutally being there. There's a decent amount of stock included and it's nice to have another 50s-60ish route to run steam and diesel together.