As noted above, the TS-112P runs QNAP's QTS 4.1 NAS OS (4.1.2 to be specific) and supports all its features, except those precluded by its reduced hardware configuration, i.e. no RAID, no video playback via HDMI, etc.
QNAP QTS Desktop
I counted 122 apps in the 112P's App center out of the 198 shown in the online App Center. The first 28 are shown below and the others are in the gallery you'll find a bit further down the page.
Some of the TS-112P supported apps
While this list is impressive, keep in mind the relatively low CPU power provided by the Marvell Kirkwood class SoC. I'm sure it will cause some of these apps to absolutely crawl.
Since it's been awhile since I reviewed single drive NASes, I had to readjust my expectations for response time when moving through the admin interface. The QTS desktop seemed to demand more from the Marvell processor than it was prepared to give.
Performance tests were run using our Revision 5 NAS test process on a single-drive volume with a 1 Gbps LAN connection. The firmware installed was QTS 4.1.2.
The TS-112P's Benchmark Summary below shows an almost 2-to-1 difference between the Windows and NASPT File copy write results, while reads are about the same. I'm not sure what caused this.
Benchmark Summary comparison
I included the DS115j's summary for easy comparison. It's clear the Synology does better than the 112P in many benchmarks, especially when it comes to large sequential file handling, as indicated by the File Copy and HD playback benches.
Since the DS115j review, we also reviewed Seagate's Personal Cloud. So with three single-drive NASes in the database, we now have something to rank! The NAS Ranker Performance Summary below shows #2 rankings for many of the benchmarks. Keep in mind when checking the rankings against the Benchmark Summaries above, that the Ranker treats values within 5% as equal. So some of the sub-rankings are ties, but aren't shown as such in the summary.
QNAP TS-112P Ranker Performance Summary
So now we can answer the Synology DS115j vs. QNAP TS-112P question. If USB 3.0 and eSATA ports are important to you, you have only one choice, the TS-112P. But for overall performance, the edge goes to Synology's DS115j. Only you can answer whether you'd rather spend the extra $10 or keep it in your pocket.