the primary difference is that Oracle database is THE Oracle product whereas Makes$h!t... has pretty much bought every software a customer may need to build its IT infrastructure. M$ bought SQL-Server from Sybase some 15 yrs ago and has been mostly tweaking the surface and technical details (like row level locking which Sybase was still missing 'til version 15); M$ bought SQL-Server in order to offer customer an upgrade path in case Access (the database software included in some M$-OFFice packages) wasn't able to handle the volume of data. instead of having to switch to Sybase, Informix, Ingres, DB2 or even Oracle, they could use a M$ product. M$ has spend quite a bit of effort in the past few years to make their version of SQL-Server look like a professional product that could play in the big boys (read DB software) league, but because M$ SQL-Server is limited to LostDOS as sole operating system it runs upon, most companies don't even bother with M$ SQL-Server. to avoid any confusion, Sybase has renamed its product ASE / Adaptive Server Enterprise about 10 yrs ago. even so, many large banks have been running Sybase SQL-Server and prize it for its stability and flexibility.
Oracle is THE database company; not because Larry Ellison invented databases or anything like it, but simply because in the past 30 yrs, Oracle (who started as a CIA software contractor) built up a pragmatic approach to data management either developing themselves more advanced solutions and utilities to manage data or, since they have become the number 1 database software company (that's easy enough, apart from Sybase there is hardly any other major software company that solely does database software...) they have also bought (smaller) competitors.
still, a good 2/3 of the S&P 500 companies (the largest quoted companies in the world) use Oracle for their data management.
and even though Oracle only does databases & All, it is still one of the largest software companies in the world.
Oracle runs on most operating systems (including Makes$h!t's LostDOS) and some companies who have grown in the last few years from small to middle or even large companies (with several hundreds of employees) and felt comfortable with LostDOS as an OS chose to use Oracle products on LostDOS.
beside databases, its core product, Oracle offers a full array of products around databases, such as web server (Oracle's own flavor of Apache) backup solutions and many enterprise applications (accounting, customer relationship, manufacturing aso.), they also increasingly so (data) management tools, like Oracle Enterprise Manager / Grid Control and, of course, Fusion.
Makes$h!t... makes #### of course, as its name indicates clearly, but in fact Makes$h!t NEVER made anything. they always only stole or cheaply bought ideas and solutions and marketed them. (SQL Server from Sybase, as mentioned earlier, NT was in fact written by an VMS engineer they hired away from DEC, based on OS/2, IE still includes in its About... the reference to Mosaic, a competitor of Netscape, 15 years ago, WordPerfect, Lotus 1-2-3 and so on, and so forth. latest mis achievement from M$? they wasted years trying to establish a search engine and eventually decided to try and buy Yahoo!...
advice? run Oracle on Linux >:)