Yes, InCollector is the closest Linux app I've seen. (I went searching for simple Linux free-form databases last year.) I just downloaded it after your mention, and I'm using it in Windows. It seems pretty smooth. I also like that it has import and export functionality. (It exports in .ied fomat, with which I'm not familiar. Maybe that's specific to Linux, but I'm using the Windows variation of InCollector. Since it's a flat database, could it just export in comma-delimited text format?)

Personally, I'd still prefer QuickDex. The main difference is that InCollector has a Title Field as well as a primary Content Field. On the input end, I prefer not having to come up with a Title or having to bother with going to an extra field to fill it in (even if I just put in X for every title). On the look-up end, you just can't beat the speed of QuickDex jumping to every instance of your character string and highlighting it. In InCollector, after you put in your search you need to scroll through your titles and open each "card" individually, then, if it's not what you want, you need to close the card and go back to scrolling and open the next possible candidate. In QuickDex, because it has just the one entry field, you just keep clicking Return and it immediately shows you the next instance of the character string in context (because of the highlighting). If you don't like that one, you just hit Return again. It's very fast. It's the simplicity itself that makes it so fast, not just that it executes instantly but it's fast in terms of the required user input (just hitting Return).