What I miss is Caesar II. I really liked that game.
When I bought my first PC in 1996, it came with a folder of CD ROMs. This impressed me at the point of sale because I didn't know any better, but they were generally useless or unappealing or both, except for Caesar II. It ran on DOS, and over the years I have made desultory attempts to get some sort of emulator working, without success. I don't really have enough knowledge to be able to troubleshoot that sort of thing.

I may have to post here a couple of times, because old favorites keep coming to mind. All-time best for the bytes- Windows Cardfile. It was nothing but alphabetical index cards, very straightforward, like a real Rolodex. Around since first Windows. Obviously,  ran super-fast on modern computers. 16-bit version still worked for me through Vista, but I need to find 32-bit version for my newest computer. This little thing ran all by itself, you could run as many versions as you wanted.

Best photo editor- Microsoft Picture-It. No kidding, could keep up with Photoshop, but was much more intuitive, had some auto-fixes better than any other program. I had Picture-It Publishing Silver 2001, a real deluxe version. CDs got lost but I think I saved iso images someplace, hope to resurrect it. BTW, later versions dumbed down, not nearly as good, but still fun. Unfortunately, totally proprietary formats, abandoned by MS.

There was a great free version of another photo program called Polyview. Only limitation was wouldn't print directly. Had some cool features, excellent easy resizing, created animated gifs, etc.

Lotus Organizer was best calendar/organizer ever, worked and looked like a paper planner. Unfortunately, old versions didn't sync well with Outlook. Wasn't aware it was still made, but just abandoned by IBM this year. Think I'm going to try to buy a copy since all these years later almost nothing still syncs with Outlook properly, anyway.

There was a great tiny planner called Plan-it Playboy. Yes, it had pictures of Playmates. Playboy made the basic version free because you were limited to 12 Playmates. They gave it free as a promo to buy the magazine, back when things worked that way. Had *great* coordination of to-do list with calendar, easily switch calendar views. The company (Anamoly Software) also made editions like Plan-It National Parks, but none caught on in the days when the first "suites" were coming out. Don't think it ran on anything later than Windows 95, maybe 98. I really hated to lose that one!

Yes, WordPerfect was always the best. You could look at a letter printed from WordPerfect next to one from Word, and always knew which was the WP one- for some reason, it looked better.

Non-PC favorite- Windows Mobile 6.0. Have it on an iPaq110 that's just dying now. It could do so many things my new Windows Phone 8 can't do. Really synched with Outlook, via simple USB. With Opera Mini, great website cruising. Even easier to type with stylus than with finger. softkeys. In fact, earlier versions of Windows Mobile/pocket PC/CE were pretty good too. All had much better adjustments for screen sensitivity, brightness controls, etc than modern devices. With a free program I could stream Web radio. And could see the screen outside in full sun, also better than modern devices.

Whoops, I realized I just switched from favorite programs to favorite devices. That'll be another thread!

Sorry for the bump, but I didn't know this topic existed for some reason. Anyway, the oldest piece of software that I use regularly is Civilization II. It's a PITA to get working on modern computers (Because the game is 16 bit, and my computer is 64 bit, I have to copy all of the files on the CD to the folder the game expects to be installed to, replace a bunch of files to upgrade it to Multiplayer Gold Edition, which is 32 bit, replace the .exe so the computer doesn't screw up democracy every turn, patch the game so it works with 64 bit computers, and run it with a special launcher to fix CPU usage and remove arbitrary in-game limits, like the amount of cities and units). Of course, it's SO worth it. I have sunk more hours into this game than any other, although SimCity 2000 comes close. It is addictive to try to beat the computer, and because the game is turn-based, you control how much time that you play. Steelpaw: Caesar II isn't available, but for $6 you can buy the sequel, Caesar 3, legitimately here: http://www.gog.com/game/caesar_3.