I bought a Roli Seaboard Rise about a year ago and it comes with Equator. Obviously it is designed to work with Roli's "5 Dimensions of Touch", which is achieved via MPE, which more hosts are supporting all the time. But don't think that means you have to have an MPE controller to use it because the VSTi works great with or without MPE.
What you get is a six oscillator synth with two multi-mode filters and more modulation options than you'll know what to do with. There are two sample-based oscillators, a noise oscillator and three V/A oscillators with around 50 different waveforms to choose from. The way it works reminds me a bit of Junglist/Hydra for those who can remember those instruments - you get a big, long list of drawn waveforms. The V/A oscillators can be used for FM, with four different algorithms on offer. Overall, it offers an incredibly broad range of options. You get a few samples when you install the instrument and there are more to download. The minimum size of the download is about 760MB and expansion pack adds another 1.2GB or so, which means you are getting a good range of high quality samples to work with.
Both filters are the same, with 13 different types available, covering all the usuals plus a comb filter and a few variations. The filters are OK, they get the job done, without really standing out.
Modulation is a stand-out feature. There are two LFO and five envelopes. The envelopes have four different modes - ADSR, ADR, ADADR and ADA-PR and, along with the LFO, can be synced to host tempo. The LFO have seven different waveforms to choose from. Beyond these features are the five dimensions of touch - STRIKE, PRESS, GLIDE, SLIDE and LIFT. You can set a response curve for each to match your playing style, giving you very fine control over how the instrument responds.
The way you add modulation is really simple - select a source, which is highlighted with an amber border, then go to the parameter you want to modlulate and adjust it's controls. The selected range will highlight in amber (normal settings are shown in blue). Once the modulation is set, the control for that parameter will animate so you can see it working. e.g. If you modulate the cutoff for Filter 1 with Envelope 2, every time you play a note, you will see the cutoff knob jump up and slide back, according to the shape of the envelope. It makes it so easy to see what's going, it is one of the most effective modulation schemes I have ever used. There is also a hidden tab with a "modulation list", which is just like the Mod Matric in many other synths.
The effects section is very good - high quality, great sounding and easy to use. There is a tab for routing everything so it's a breeze to set up complex signal paths to take full advantage of the effects. It's also where you can turn the overall volume of a patch up/down. The final tab is for global settings.
It's not perfect, though, The windows where you adjust the envelopes are far too small, making it hard to get precise values. At least you can zoom the 5D response curve windows (another tab). To be honest, I'd have preferred just two or three envelopes with bigger windows. CPU use is more than reasonable for what's on offer - 3% to 6% for a single voice on my Core i5 2-in-1 and 6-11% for a three note chord.
Overall, Roli have put a lot of effort into making Equator extremely powerful, yet easy to use in a way many other developers struggle to deliver. Almost everything is visible on the front panel, which can be resized by grabbing the bottom-right corner and pulling (it only gets bigger) and those things that are hidden behind tabs are all things you hardly ever need to see. The sound quality is stellar and using it as it is meant to be used, with a Seaboard controller, makes for an expressive experience out of the box that's pretty much unbeatable. But if you want to buy it as a standalone product, you won't get the full experience, which makes it's asking price very steep. If you ever see it for $99, grab it, otherwise think carefully before making a decision.