Some tower defense games are hit or miss for me, but the upgrade tree on this and the various achievement distinctions (Brilliant Rating for not letting anyone TOUCH your gems) make this a great time sink.
Starland Multiplayer TD exists. It's not exactly what you want, as both people play defenders.
I played this for hours when it first came out, but unsure how many people would still be active on it.
I'm the dev of Dodge Drop, an evasion game where you must fall to the bottom while avoiding most of the obstacles. The game is fairly simple and easy, and you can turn on Easy Mode if you have to.
I upgraded my crappy old desktop computer with a gig of RAM from Newegg.com for forty bucks a couple of months ago, and it made a world of difference. I have since found compatible RAM on eBay for twenty and thirty bucks. You need to know what kind of RAM your computer requires, but Newegg has a process to help you figure it out, and some of the big memory vendors on eBay will know what you need, too.
RAM for newer computers seems to be cheaper.
You should google the game title and put it on other website. The author receives some money, when game is frequently played on another websites. I found it here: http://www.newgrounds.com/portal/view/237765
Nice atmosphere, but too simple gameplay for me.
Am I allowed to suggest the site I post my own games on?
If so: AirConsole :D
It's a browser-based gaming platform controlled by smartphone with a focus on local multiplayer games.
I've sunk hours and hours into Bubble Spinner while listening to Audiobooks in the past few months.
I play it on iOS, but it doesn't seem to be available in the store anymore, I could just re-download it via my account.
Here's the web version though.
My personal High Score is about 50k :D
Btw, another way to keep my hands busy while listening: Microsoft Solitaire Collection, mainly Free Cell.
Here's the multi-player section of Kongregate.
Starland TD is a pretty good 1v1 TD game, as long as you're playing someone of similar skill level.
Kongregate.com has a very wholesome site, and the guy who runs it and his sister are both redditors.
Many games she may like are there, such as Toss the Turtle, and Dolphin Olympics.
I believe it's Flight. It's a popular game; you can find it pretty easily on any major game site...which is probably why it wasn't linked in /r/webgames
The second one might be The Last Door which now has 3 parts plus a prologue. (I gave up after part 1 because of excessive text instead of atmosphere.)
There's a lot of range in them. Some of them are just the simple "click, buy thing, wait for thing to make more money, buy more thing" type. But something like Anti-Idle has (ridiculously) much more.
Papa's Taco Mia! seems to be what you're looking for. It seems they've also released other games based on the same concept (Papa's Burgeria/Pizzeria/etc)
Don't really know what they're called though.
Upgrade Complete - a satirical look at upgrade games
Ooh, now it looks like there's an Upgrade Complete 2